<PAGE>
   AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON FEBRUARY   , 2000

                                                      REGISTRATION NO. 333-
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                            ------------------------

                                    FORM S-8
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933
                            ------------------------

                         FLAG TELECOM HOLDINGS LIMITED
             (Exact name of Registrant as specified in its charter)

                         ------------------------------

                               EMPORIUM BUILDING
                                69 FRONT STREET
                                    HAMILTON
                                 HM 12 BERMUDA
         (Address, including zip code, of Principal Executive Offices)
                         ------------------------------

                         FLAG TELECOM HOLDINGS LIMITED
                            LONG-TERM INCENTIVE PLAN
                            (Full Title of the Plan)
                         ------------------------------

                             FLAG TELECOM USA LTD.
                              570 LEXINGTON AVENUE
                            NEW YORK, NEW YORK 10020
                                 (212)319-2121
(Name, address, and telephone number, including area code, of agent for service)
                         ------------------------------

                                    COPY TO:
                             DAVID W. POLLAK, ESQ.
                          MORGAN, LEWIS & BOCKIUS LLP
                                101 PARK AVENUE
                            NEW YORK, NEW YORK 10178
                                 (212) 309-6000
                              FAX: (212) 309-6273
                            ------------------------

                        CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
                                                              PROPOSED MAXIMUM     PROPOSED MAXIMUM
                                         NUMBER OF SHARES      OFFERING PRICE          AGGREGATE            AMOUNT OF
 TITLE OF SECURITIES TO BE REGISTERED   TO BE REGISTERED(1)       PER SHARE         OFFERING PRICE     REGISTRATION FEE(4)
<S>                                     <C>                  <C>                  <C>                  <C>
Common Stock, $.0006 par value per
  share                                       135,833            $ 11.04(2)           $ 1,499,600           $  395.89
                                             3,966,873           $  6.42(2)           $25,467,325          $ 6,723.37
                                             2,661,085           $31.125(3)           $82,826,270          $21,866.13
Total.................................       6,763,791                                                     $28,985.39
</TABLE>

(1) Pursuant to Rule 416(a), the number of shares being registered shall include
    an indeterminate number of additional shares of common stock or common stock
    which may become issuable as a result of stock splits, stock dividends, or
    similar transactions in accordance with anti-dilution provisions of the
    Long-Term Incentive Plan.

(2) Calculated pursuant to Rule 457(h) for the purpose of calculating the
    registration fee, based upon the price at which outstanding options under
    the Long-Term Incentive Plan may be exercised.

(3) Calculated pursuant to Rules 457(c) and (h), based upon the average of the
    high and low prices reported on the Nasdaq National Market for February 14,
    2000.

(4) Calculated pursuant to Section 6(b) of the Securities Act of 1933 as
    follows: Proposed maximum aggregate offering price per share multiplied by
    .000264.

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
<PAGE>
                                     PART I
              INFORMATION REQUIRED IN THE SECTION 10(A) PROSPECTUS

ITEM 1.  PLAN INFORMATION.*

ITEM 2.  REGISTRANT INFORMATION AND EMPLOYEE PLAN ANNUAL INFORMATION.*

    *   Information required by Part I to be contained in the Section 10(a)
       prospectus is omitted from this registration statement in accordance with
       Rule 428 under the Securities Act of 1933, as amended (the "ACT"), and
       the Explanatory Note to Part I of this Registration Statement on
       Form S-8.
<PAGE>
PROSPECTUS

                                  6,763,791 SHARES

                         FLAG TELECOM HOLDINGS LIMITED

                                  COMMON STOCK

                               ------------------

    We are a global carriers' carrier that develops and offers a broad range of
telecommunications products and services to licensed international carriers,
Internet service providers and other telecommunications companies. This
prospectus relates to the resale of our common stock by our officers and
directors and others who may be in a control relationship with us and by certain
of our employees. The common stock which may be sold has previously been
acquired, or will be acquired, by these individuals upon exercise of options
granted to them under the FLAG Telecom Holdings Limited Long-Term Incentive
Plan, which became effective February 26, 1999.

    We will not receive any of the proceeds from these sales. We will pay all
expenses in connection with this offering, other than commissions and discounts
of underwriters, dealers or agents.

    Our common stock is quoted on the Nasdaq National Market (Symbol: FTHL), and
on the London Stock Exchange (Symbol: FTL). On February 14, 2000, the closing
price of the common stock was $30.63 per share.

    Neither the Securities and Exchange Commission (the ``SEC") nor any state
securities commission has approved or disapproved of these securities or
determined if this prospectus is truthful or complete. Any representation to the
contrary is a criminal offense.

                  The date of this prospectus is February 16, 2000
<PAGE>
    We have not, nor has any individual named in this prospectus, authorized any
person to give any information or to make any representation other than those
contained in, or incorporated by reference into, this prospectus. This
prospectus does not constitute an offer to sell or solicitation of an offer to
buy.

    We have filed a registration statement on Form S-8 in respect of the common
stock offered by this prospectus with the SEC under the Securities Act of 1933
(the ``Securities Act"). This prospectus does not contain all of the information
contained in the registration statement. You should read this entire prospectus
carefully as well as the registration statement for additional information.

                      WHERE YOU CAN FIND MORE INFORMATION

    We file annual, quarterly and special reports, proxy statements and other
information with the SEC. You may read and copy any documents we file at the
SEC's public reference rooms in Washington, D.C., New York, N.Y. and Chicago,
Illinois. Please call the SEC at 1-800-SEC-0330 for further information on the
public reference rooms. Our SEC filings are also available to the public from
the SEC's web site at http://www.sec.gov.

    The SEC allows us to "incorporate by reference" information into this
prospectus, which means that we can disclose important information to you by
referring you to another document filed separately with the SEC. The information
incorporated by reference is considered to be part of this prospectus.
Information in this prospectus may update documents previously filed with the
SEC, and later information that we file with the SEC will automatically update
this prospectus. We incorporate by reference the documents listed below and any
future filings made with the SEC under Section 13(a), 13(c), 14 or 15(d) of the
Securities Exchange Act of 1934 (the ``Exchange Act") prior to the termination
of the offering:

    - Our Registration Statement on Form F-1 (Registration No. 333-94899) filed
      with the SEC on January 18, 2000, Amendment No. 1 thereto, filed
      February 3, 2000, Amendment No. 2 thereto, filed February 7, 2000, and
      Amendment No. 3 thereto, filed February 9, 2000;

    - Our prospectus contained in the Registration Statement on Form F-1
      (Registration No. 333-94899), filed pursuant to Rule 424(b) under the
      Securities Act on January 18, 2000 for the offering of 26,400,000 shares
      of common stock, and later amended to reflect the offering of 31,680,000
      shares of common stock; and

    - Our Form 8-A (Registration Number 000-29207) filed on January 27, 2000,
      including any amendments or reports filed for the purpose of updating the
      description of our common stock that is incorporated by reference therein.

    You may request a copy of these filings at no cost, by writing or
telephoning us at the following address:

                         FLAG TELECOM HOLDINGS LIMITED
                               EMPORIUM BUILDING
                                69 FRONT STREET
                                 HAMILTON HM 12
                                    BERMUDA
                              ATTENTION: SECRETARY
                                 (441) 296-0909

                            ------------------------

    Our websites are http://www.flagtelecom.com and http://www.flagatlantic.com.
Information on our website is not part of this prospectus.

                                       2
<PAGE>
                                  OUR BUSINESS

    We are a global carriers' carrier that develops and offers a broad range of
telecommunications products and services to licensed international carriers,
Internet service providers and other telecommunications companies. We have an
established customer base of approximately 90 customers, many of which are among
the world's leading telecommunications and Internet companies. Our customers
include 17 of the top 20 international carriers based on traffic volume which,
together, accounted for approximately 48% of our sales to date. We believe we
have succeeded in attracting this customer base primarily as the result of the
diversity, flexibility and high quality of our product and service offerings.
Our goal is to establish FLAG Telecom as the leading global carriers' carrier by
offering a wide range of cost-effective capacity use options and wholesale
products and services across our global network. We also plan to develop an
extensive range of innovative products and services which will use a
state-of-the-art Internet Protocol-based network infrastructure.

                                    PROCEEDS

    We will not receive any of the proceeds from the sale of the shares of our
common stock by the individuals named herein.

                                       3
<PAGE>
                              SELLING STOCKHOLDERS

    The individuals who may use this prospectus to sell our common stock are our
officers, directors and others who may be in a control relationship with us as
well as certain of our current and former employees. The shares listed below
will not be transferable until August 9, 2000. We do not know whether the
individuals listed below will sell any or all of their shares covered by this
prospectus.

<TABLE>
<CAPTION>
                                                                                 NUMBER OF SHARES
                                                              NUMBER OF SHARES   COVERED BY THIS
SELLING STOCKHOLDER                                               OWNED(1)          PROSPECTUS
-------------------                                           ----------------   ----------------
<S>                                                           <C>                <C>
Andres Bande................................................     1,071,701          1,071,701
Edward McCormack............................................       318,000            318,000
Stuart Rubin................................................       293,000            293,000
Michael Fitzpatrick.........................................        41,667             41,667
Abdul Latif Ghurab..........................................        41,667             41,667
Adnan Omar..................................................        41,667             41,667
Daniel Petri................................................        41,667             41,667
Umberto Silvestri...........................................        41,667             41,667
Jonathan Solomon............................................        41,667             41,667
Dr. Lim Lek Suan............................................        41,667             41,667
Fumio Uehara................................................        41,667             41,667
Dr. Vallobh Vimolvanich.....................................        41,667             41,667
</TABLE>

------------------------

(1) Based on ownership as of February 11, 2000. Includes shares issuable to the
    named individuals upon exercise of currently outstanding options under the
    FLAG Telecom Holdings Limited Long-Term Incentive Plan, whether or not
    presently exercisable.

                                       4
<PAGE>
                              PLAN OF DISTRIBUTION

    The shares of our common stock covered by this prospectus will be sold, if
at all, by the individuals named above, and not by us. The shares may be sold
from time to time as follows:

    - on the Nasdaq National Market, in the over-the-counter market, or on a
      national securities exchange (any of which may involve crosses and block
      transactions);

    - to purchasers directly;

    - in ordinary brokerage transactions in which the broker solicits
      purchasers;

    - through underwriters, dealers and agents who may receive compensation in
      the form of underwriting discounts, concessions or commissions from a
      seller and/or the purchasers of the shares for whom they may act as agent;

    - through the writing of options on the shares;

    - through the pledge of shares as security for any loan or obligation,
      including pledges to brokers or dealers who may from time to time effect
      distributions of the shares or other interests in the shares;

    - through purchases by a broker or dealer as principal and resale by such
      broker or dealer for its own account pursuant to this prospectus;

    - through block trades in which the broker or dealer so engaged will attempt
      to sell the shares as agent or as riskless principal but may position and
      resell a portion of the block as principal to facilitate the transaction;

    - through exchange distributions in accordance with the rules of the
      applicable exchange;

    - in any combination of one or more of these methods; or

    - in any other lawful manner.

    These sales may be made at prices related to the then current market price
or otherwise at prices and on terms then prevailing, or in privately negotiated
transactions. In effecting sales, a broker or dealer engaged by an individual
using this prospectus to sell common stock may arrange for other brokers or
dealers to participate in the sale. In addition, any shares covered by this
prospectus which qualify for sale pursuant to Section 4(l) of the Securities Act
or Rules 144 or 701(g) under the Securities Act may be sold thereunder rather
than by this prospectus.

    The number of shares to be reoffered or resold by means of this prospectus
by each individual named above, and any other individual with whom he or she is
cooperating for the purpose of selling our common stock, may not exceed the
greater of, during any three-month period, (1) 1% of all outstanding shares of
our common stock, (2) the average weekly reported volume of trading in our
common stock on the Nasdaq National Market during the four weeks preceding the
date of the receipt of the order to execute the transaction by the broker or the
date of execution of the transaction directly with a market maker, or (3) the
average weekly volume of trading in our common stock reported through the
consolidated transaction reporting system contemplated by Rule 11Aa3-1 under the
Exchange Act during the four-week period specified in clause (ii) above.

    In connection with distributions of the shares or otherwise, an individual
using this prospectus to sell common stock may enter into hedging transactions
with a broker-dealer. In connection with such a transaction, a broker-dealer may
engage in short sales of shares registered hereunder in the course of hedging
the positions they assume with the seller. The seller may also sell shares short
and deliver the shares to close out such short positions. The seller may also
enter into an option or other transaction

                                       5
<PAGE>
with a broker-dealer which requires the delivery to the broker-dealer of shares
we have registered, which the broker-dealer may resell by this prospectus.

    A seller may pay a broker-dealer or an agent compensation in the form of
commissions, discounts or concessions. The broker-dealer and any other
participating broker-dealer may be deemed to be "underwriters" within the
meaning of the Securities Act in connection with such sales and any such
commission, discount or concession may be deemed to be underwriting discounts or
commissions under the Securities Act.

    We may be required to file a supplemented prospectus in connection with any
activities involving a seller which may be deemed to be an "underwriting." In
that case, a supplement to this prospectus would contain (1) information as to
whether an underwriter selected by a seller, or any other broker-dealer, is
acting as principal or agent for the seller, (2) the compensation to be received
by an underwriter selected by a seller or any broker-dealer, for acting as
principal or agent for a seller and (3) the compensation to be received by any
other broker-dealer, in the event the compensation of such other broker-dealers
is in excess of usual and customary commissions. Any broker or dealer
participating in any distribution of the shares may be required to deliver a
copy of this prospectus, including any prospectus supplement, to any individual
who purchases any shares from or through such a broker-dealer.

    We have advised the people identified in this prospectus as potential
sellers of common stock that during any period when they may be engaged in a
distribution of the shares offered by this prospectus, they are required to
comply with Regulation M promulgated under the Exchange Act. With certain
exceptions, Regulation M precludes any seller, any affiliated purchaser and any
broker-dealer or other individual who participates in such a distribution from
bidding for or purchasing, or attempting to induce any individual to bid for or
purchase any security, that is the subject of the distribution until the entire
distribution is complete. Regulation M also prohibits any bids or purchases made
in order to stabilize the price of a security in connection with the
distribution of that security. All of these factors may affect the marketability
of our common stock.

    The people identified in this prospectus as potential sellers of common
stock offer to sell all, some or none of the shares covered by this prospectus.
Because it is possible that a significant number of shares could be sold
simultaneously by means of this prospectus, such sales, or the possibility
thereof, may have an adverse effect on the market price of our common stock.

                                INDEMNIFICATION

    Our By-Laws provide that our directors and officers and former directors and
officers shall be indemnified to the fullest extent permitted by The Companies
Act of Bermuda 1981, as amended from time to time, and provides for advances to
any indemnified director or officer of expenses in connection with actual
proceedings and claims arising out of their status as our director or officer.
We also maintain a directors' and officers' liability insurance policy on behalf
of our directors and officers.

                            VALIDITY OF COMMON STOCK

    The validity of our common shares will be passed on by Appleby, Spurling &
Kempe, Hamilton, Bermuda.

                                       6
<PAGE>
                                    EXPERTS

    The financial statements and schedules of FLAG Telecom Holdings Limited for
the period of incorporation to September 30, 1999 and FLAG Limited for the
period from January 1, 1999 to February 26, 1999 and for the years ended
December 31, 1998, 1997 and 1996, incorporated in this prospectus by reference
to our prospectus dated January 18, 2000, have been so incorporated in reliance
on the report of Arthur Andersen & Co., independent accountants, as indicated in
their reports with respect thereto, and are included herein in reliance on the
authority of said firm as experts in giving said reports.

                                       7
<PAGE>
                                    PART II
               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

    The following documents filed by us with the Securities and Exchange
Commission ("SEC") are incorporated by reference into this Registration
Statement:

        (a) Our Registration Statement on Form F-1 (Registration No. 333-94899)
    filed with the SEC on January 18, 2000, Amendment No. 1 to such Registration
    Statement, filed February 3, 2000, Amendment No. 2 to such Registration
    Statement, filed February 7, 2000, and Amendment No. 3 to such Registration
    Statement, filed February 9, 2000.

        (b) The description of our Common Stock, par value $.0006 per Share,
    contained in its Registration Statement on Form 8-A (Registration
    No. 000-29207) filed with the SEC on January 27, 2000, including any
    amendment or report filed for the purpose of updating such description.

    All reports and other documents subsequently filed by us pursuant to
Section 13(a), 13(c), 14 or 15(d) of the Exchange Act prior to the filing of a
post-effective amendment which indicates that all securities offered have been
sold or which deregisters all securities then remaining unsold shall be deemed
to be incorporated by reference in this Registration Statement and to be a part
hereof from the date of filing of such documents.

    Any statement contained herein or in a document all or a portion of which is
incorporated or deemed to be incorporated by reference herein shall be deemed to
be modified or superseded for purposes of this Registration Statement to the
extent that a statement contained herein or in any other subsequently filed
document which also is or is deemed to be incorporated by reference herein
modifies or supersedes such statement. Any such statement so modified or
superseded shall not be deemed, except as so modified or superseded, to
constitute a part of this Registration Statement.

                                    EXPERTS

    The financial statements and schedules of FLAG Telecom Holdings Limited for
the period from incorporation to September 30, 1999 and FLAG Limited for the
period from January 1, 1999 to February 26, 1999 and for the years ended
December 31, 1998, 1997 and 1996 incorporated by reference in this Registration
Statement have been audited by Arthur Andersen & Co., independent public
accountants, as indicated in their reports with respect thereto, and are
included herein in reliance the authority of said firm as experts in giving said
reports.

ITEM 4.  DESCRIPTION OF SECURITIES.

    Not Applicable.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

    Not Applicable.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

    Our By-Laws provide that our directors and officers and former directors and
officers shall be indemnified to the fullest extent permitted by The Companies
Act of Bermuda 1981, as amended from time to time, and provides for advances to
any indemnified director or officer of expenses in connection with actual
proceedings and claims arising out of their status as our director or officer.
We also maintain a directors' and officers' liability insurance policy on behalf
of our directors and officers.

                                      II-1
<PAGE>
ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

    Not Applicable.

ITEM 8.  EXHIBITS.

<TABLE>
<CAPTION>
EXHIBIT                 DESCRIPTION
-------                 -----------
<S>                     <C>
 4.1                    Memorandum of Association, incorporated by reference to
                        exhibit 3.1 to our Registration Statement on Form F-1,
                        Registration No. 333-94899, filed with the SEC on
                        January 18, 2000.

 4.2                    By-Laws of FLAG Telecom Holdings Limited, incorporated by
                        reference to exhibit 3.2 to our Registration Statement on
                        Form F-1 (Registration No. 333-94899) filed with the SEC on
                        January 18, 2000.

 4.3                    FLAG Telecom Holdings Limited Long-Term Incentive Plan,
                        incorporated by reference to exhibit 10.1 to our
                        Registration Statement on Form F-1 (Registration
                        No. 333-94899) filed with the SEC on January 18, 2000.

 5.1                    Opinion of Appleby Spurling & Kempe.

 23.1                   Consent of Arthur Andersen & Co.

 23.3                   Consent of Appleby Spurling & Kempe (included in
                        Exhibit 5.1).

 24                     Powers of Attorney (included on page II-4 of this
                        Registration Statement).
</TABLE>

ITEM 9.  UNDERTAKINGS.

    (a) The undersigned registrant hereby undertakes:

        (1) To file, during any period in which offers or sales are being made,
    a post-effective amendment to this Registration Statement:

           (i) To include any prospectus required by Section 10(a)(3) of the
       Securities Act;

           (ii) To reflect in the Prospectus any facts or events arising after
       the effective date of this Registration Statement (or the most recent
       post-effective amendment thereof) which, individually or in the
       aggregate, represent a fundamental change in the information set forth in
       this Registration Statement; and

           (iii) To include any material information with respect to the plan of
       distribution not previously disclosed in this Registration Statement or
       any material change to such information in this Registration Statement;

PROVIDED, HOWEVER, that paragraphs (a)(1)(i) and (a)(1)(ii) do not apply if the
information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed by the registrant pursuant to
Section 13 or Section 15(d) of the Exchange Act that are incorporated by
reference in this Registration Statement.

        (2) That, for the purpose of determining any liability under the
    Securities Act, each such post-effective amendment shall be deemed to be a
    new registration statement relating to the securities offered therein, and
    the offering of such securities at that time shall be deemed to be the
    initial bona fide offering thereof.

        (3) To remove from registration by means of a post-effective amendment
    any of the securities being registered which remain unsold at the
    termination of the offering.

                                      II-2
<PAGE>
    (b) The undersigned registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to Section 15(d) of the Exchange Act) that is
incorporated by reference in the Registration Statement shall be deemed to be a
new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

    (c) Insofar as indemnification for liabilities arising under the Securities
Act may be permitted to directors, officers and controlling persons of the
registrant pursuant to the foregoing provisions, or otherwise, the registrant
has been advised that in the opinion of the SEC such indemnification is against
public policy as expressed in the Securities Act and is, therefore,
unenforceable. In the event that a claim for indemnification against such
liabilities (other than the payment by the registrant of expenses incurred or
paid by a director, officer or controlling person of the registrant in the
successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.

                                      II-3
<PAGE>
                                   SIGNATURES

    Pursuant to the requirements of the Securities Act of 1933, the registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of London, England, on February 16, 2000.

<TABLE>
<S>                                                    <C>  <C>
                                                       FLAG TELECOM HOLDINGS LIMITED

                                                       By:  /s/ STUART RUBIN
                                                            -----------------------------------------
                                                            Name: Stuart Rubin
                                                            Title: General Counsel and Assistant
                                                            Secretary
</TABLE>

    Each person whose signature appears below constitutes and appoints Andres
Bande, Edward McCormack and Stuart Rubin, and each of them, with full power to
act without the other, this person's true and lawful attorneys-in-fact and
agents, with full power of substitution and resubstitution, for him and in his
name, place and stead, in any and all capacities, to sign any and all amendments
(including post-effective amendments) to this Registration Statement and any and
all other documents and instruments incidental thereto, and to file the same,
with all exhibits thereto, and all documents in connection therewith, with the
Securities and Exchange Commission and any other regulatory authority, granting
unto said attorneys-in-fact and agents, and each of them, full power and
authority to do and perform each and every act and thing requisite and necessary
to be done, as fully to all intents and purposes as he might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents, or any of them, or his substitute, may lawfully do or cause to be done
by virtue hereof.

    Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed below by the following individuals in the
capacities and on the dates indicated.

<TABLE>
<CAPTION>
                    NAME                                     TITLE                        DATE
                    ----                                     -----                        ----
<C>                                            <S>                                 <C>
              /s/ ANDRES BANDE                 Chairman and Chief Executive
    ------------------------------------         Officer (Principal Executive      February 16 , 2000
                Andres Bande                     Officer)

            /s/ EDWARD MCCORMACK
    ------------------------------------       Chief Financial Officer (Principal  February 16, 2000
              Edward McCormack                   Financial Officer)

              /s/ STUART RUBIN
    ------------------------------------       General Counsel and Assistant       February 16, 2000
                Stuart Rubin                     Secretary

           /s/ MICHAEL FITZPATRICK
    ------------------------------------       Director                            February 16, 2000
             Michael Fitzpatrick

            /s/ EDWARD J. MCQUAID
    ------------------------------------       Director                            February 16, 2000
              Edward J. McQuaid

               /s/ ADNAN OMAR
    ------------------------------------       Director                            February 16, 2000
                 Adnan Omar

              /s/ DANIEL PETRI
    ------------------------------------       Director                            February 16, 2000
                Daniel Petri
</TABLE>

                                      II-4
<PAGE>
<TABLE>
<C>                                            <S>                                 <C>
              /s/ PHILIP SESKIN
    ------------------------------------       Director                            February 16, 2000
                Philip Seskin

            /s/ UMBERTO SILVESTRI
    ------------------------------------       Director                            February 16, 2000
              Umberto Silvestri

            /s/ JONATHAN SOLOMON
    ------------------------------------       Director                            February 16, 2000
              Jonathan Solomon

         /s/ DR. VALLOBH VIMOLVANICH
    ------------------------------------       Director                            February 16, 2000
           Dr. Vallobh Vimolvanich

             /s/ LARRY BAUTISTA
    ------------------------------------       Authorized US Representative        February 16, 2000
               Larry Bautista
</TABLE>

                                      II-5
<PAGE>
                                 EXHIBIT INDEX

<TABLE>
<CAPTION>
EXHIBIT                 DESCRIPTION
-------                 -----------
<S>                     <C>
 4.1                    Memorandum of Association, incorporated by reference to
                        exhibit 3.1 to our Registration Statement on Form F-1
                        (Registration No. 333-94899) filed with the SEC on
                        January 18, 2000.

 4.2                    By-Laws of FLAG Telecom Holdings Limited, incorporated by
                        reference to exhibit 3.2 to our Registration Statement on
                        Form F-1 (Registration No. 333-94899) filed with the SEC on
                        January 18, 2000.

 4.3                    FLAG Telecom Holdings Limited Long-Term Incentive Plan,
                        incorporated by reference to exhibit 10.1 to our
                        Registration Statement on Form F-1 (Registration
                        No. 333-94899) filed with the SEC on January 18, 2000.

 5.1                    Opinion of Appleby Spurling & Kempe.

 23.1                   Consent of Arthur Andersen & Co.

 23.3                   Consent of Appleby Spurling & Kempe (included in
                        Exhibit 5.1).

 24                     Powers of Attorney (included on page II-4 of this
                        Registration Statement).
</TABLE>
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{"company-data": {"conformed-name": "FLAG TELECOM HOLDINGS LTD", "cik": "0001102752", "assigned-sic": "4813", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-30550", "film-number": "547688"}, "business-address": {"street1": "EMPORIUM BLDG", "street2": "69 FRONT STREET", "city": "HAMILTON BERMUDA"}, "mail-address": {"street1": "EMPORIUM BLDG", "street2": "69 FRONT STREET", "city": "HAMILTON BERMUDA"}}
AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON FEBRUARY   , 2000

                                                      REGISTRATION NO. 333-
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                            ------------------------

                                    FORM S-8
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933
                            ------------------------

                         FLAG TELECOM HOLDINGS LIMITED
             (Exact name of Registrant as specified in its charter)

                         ------------------------------

                               EMPORIUM BUILDING
                                69 FRONT STREET
                                    HAMILTON
                                 HM 12 BERMUDA
         (Address, including zip code, of Principal Executive Offices)
                         ------------------------------

                         FLAG TELECOM HOLDINGS LIMITED
                            LONG-TERM INCENTIVE PLAN
                            (Full Title of the Plan)
                         ------------------------------

                             FLAG TELECOM USA LTD.
                              570 LEXINGTON AVENUE
                            NEW YORK, NEW YORK 10020
                                 (212)319-2121
(Name, address, and telephone number, including area code, of agent for service)
                         ------------------------------

                                    COPY TO:
                             DAVID W. POLLAK, ESQ.
                          MORGAN, LEWIS & BOCKIUS LLP
                                101 PARK AVENUE
                            NEW YORK, NEW YORK 10178
                                 (212) 309-6000
                              FAX: (212) 309-6273
                            ------------------------

                        CALCULATION OF REGISTRATION FEE
PROPOSED MAXIMUM     PROPOSED MAXIMUM
                                         NUMBER OF SHARES      OFFERING PRICE          AGGREGATE            AMOUNT OF
 TITLE OF SECURITIES TO BE REGISTERED   TO BE REGISTERED(1)       PER SHARE         OFFERING PRICE     REGISTRATION FEE(4)
Common Stock, $.0006 par value per
  share                                       135,833            $ 11.04(2)           $ 1,499,600           $  395.89
                                             3,966,873           $  6.42(2)           $25,467,325          $ 6,723.37
                                             2,661,085           $31.125(3)           $82,826,270          $21,866.13
Total.................................       6,763,791                                                     $28,985.39
(1) Pursuant to Rule 416(a), the number of shares being registered shall include
    an indeterminate number of additional shares of common stock or common stock
    which may become issuable as a result of stock splits, stock dividends, or
    similar transactions in accordance with anti-dilution provisions of the
    Long-Term Incentive Plan.

(2) Calculated pursuant to Rule 457(h) for the purpose of calculating the
    registration fee, based upon the price at which outstanding options under
    the Long-Term Incentive Plan may be exercised.

(3) Calculated pursuant to Rules 457(c) and (h), based upon the average of the
    high and low prices reported on the Nasdaq National Market for February 14,
    2000.

(4) Calculated pursuant to Section 6(b) of the Securities Act of 1933 as
    follows: Proposed maximum aggregate offering price per share multiplied by
    .000264.

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
PART I
              INFORMATION REQUIRED IN THE SECTION 10(A) PROSPECTUS

ITEM 1.  PLAN INFORMATION.*

ITEM 2.  REGISTRANT INFORMATION AND EMPLOYEE PLAN ANNUAL INFORMATION.*

    *   Information required by Part I to be contained in the Section 10(a)
       prospectus is omitted from this registration statement in accordance with
       Rule 428 under the Securities Act of 1933, as amended (the "ACT"), and
       the Explanatory Note to Part I of this Registration Statement on
       Form S-8.
PROSPECTUS

                                  6,763,791 SHARES

                         FLAG TELECOM HOLDINGS LIMITED

                                  COMMON STOCK

                               ------------------

    We are a global carriers' carrier that develops and offers a broad range of
telecommunications products and services to licensed international carriers,
Internet service providers and other telecommunications companies. This
prospectus relates to the resale of our common stock by our officers and
directors and others who may be in a control relationship with us and by certain
of our employees. The common stock which may be sold has previously been
acquired, or will be acquired, by these individuals upon exercise of options
granted to them under the FLAG Telecom Holdings Limited Long-Term Incentive
Plan, which became effective February 26, 1999.

    We will not receive any of the proceeds from these sales. We will pay all
expenses in connection with this offering, other than commissions and discounts
of underwriters, dealers or agents.

    Our common stock is quoted on the Nasdaq National Market (Symbol: FTHL), and
on the London Stock Exchange (Symbol: FTL). On February 14, 2000, the closing
price of the common stock was $30.63 per share.

    Neither the Securities and Exchange Commission (the ``SEC") nor any state
securities commission has approved or disapproved of these securities or
determined if this prospectus is truthful or complete. Any representation to the
contrary is a criminal offense.

                  The date of this prospectus is February 16, 2000
We have not, nor has any individual named in this prospectus, authorized any
person to give any information or to make any representation other than those
contained in, or incorporated by reference into, this prospectus. This
prospectus does not constitute an offer to sell or solicitation of an offer to
buy.

    We have filed a registration statement on Form S-8 in respect of the common
stock offered by this prospectus with the SEC under the Securities Act of 1933
(the ``Securities Act"). This prospectus does not contain all of the information
contained in the registration statement. You should read this entire prospectus
carefully as well as the registration statement for additional information.

                      WHERE YOU CAN FIND MORE INFORMATION

    We file annual, quarterly and special reports, proxy statements and other
information with the SEC. You may read and copy any documents we file at the
SEC's public reference rooms in Washington, D.C., New York, N.Y. and Chicago,
Illinois. Please call the SEC at 1-800-SEC-0330 for further information on the
public reference rooms. Our SEC filings are also available to the public from
the SEC's web site at http://www.sec.gov.

    The SEC allows us to "incorporate by reference" information into this
prospectus, which means that we can disclose important information to you by
referring you to another document filed separately with the SEC. The information
incorporated by reference is considered to be part of this prospectus.
Information in this prospectus may update documents previously filed with the
SEC, and later information that we file with the SEC will automatically update
this prospectus. We incorporate by reference the documents listed below and any
future filings made with the SEC under Section 13(a), 13(c), 14 or 15(d) of the
Securities Exchange Act of 1934 (the ``Exchange Act") prior to the termination
of the offering:

    - Our Registration Statement on Form F-1 (Registration No. 333-94899) filed
      with the SEC on January 18, 2000, Amendment No. 1 thereto, filed
      February 3, 2000, Amendment No. 2 thereto, filed February 7, 2000, and
      Amendment No. 3 thereto, filed February 9, 2000;

    - Our prospectus contained in the Registration Statement on Form F-1
      (Registration No. 333-94899), filed pursuant to Rule 424(b) under the
      Securities Act on January 18, 2000 for the offering of 26,400,000 shares
      of common stock, and later amended to reflect the offering of 31,680,000
      shares of common stock; and

    - Our Form 8-A (Registration Number 000-29207) filed on January 27, 2000,
      including any amendments or reports filed for the purpose of updating the
      description of our common stock that is incorporated by reference therein.

    You may request a copy of these filings at no cost, by writing or
telephoning us at the following address:

                         FLAG TELECOM HOLDINGS LIMITED
                               EMPORIUM BUILDING
                                69 FRONT STREET
                                 HAMILTON HM 12
                                    BERMUDA
                              ATTENTION: SECRETARY
                                 (441) 296-0909

                            ------------------------

    Our websites are http://www.flagtelecom.com and http://www.flagatlantic.com.
Information on our website is not part of this prospectus.

                                       2
OUR BUSINESS

    We are a global carriers' carrier that develops and offers a broad range of
telecommunications products and services to licensed international carriers,
Internet service providers and other telecommunications companies. We have an
established customer base of approximately 90 customers, many of which are among
the world's leading telecommunications and Internet companies. Our customers
include 17 of the top 20 international carriers based on traffic volume which,
together, accounted for approximately 48% of our sales to date. We believe we
have succeeded in attracting this customer base primarily as the result of the
diversity, flexibility and high quality of our product and service offerings.
Our goal is to establish FLAG Telecom as the leading global carriers' carrier by
offering a wide range of cost-effective capacity use options and wholesale
products and services across our global network. We also plan to develop an
extensive range of innovative products and services which will use a
state-of-the-art Internet Protocol-based network infrastructure.

                                    PROCEEDS

    We will not receive any of the proceeds from the sale of the shares of our
common stock by the individuals named herein.

                                       3
SELLING STOCKHOLDERS

    The individuals who may use this prospectus to sell our common stock are our
officers, directors and others who may be in a control relationship with us as
well as certain of our current and former employees. The shares listed below
will not be transferable until August 9, 2000. We do not know whether the
individuals listed below will sell any or all of their shares covered by this
prospectus.
NUMBER OF SHARES
                                                              NUMBER OF SHARES   COVERED BY THIS
SELLING STOCKHOLDER                                               OWNED(1)          PROSPECTUS
-------------------                                           ----------------   ----------------
Andres Bande................................................     1,071,701          1,071,701
Edward McCormack............................................       318,000            318,000
Stuart Rubin................................................       293,000            293,000
Michael Fitzpatrick.........................................        41,667             41,667
Abdul Latif Ghurab..........................................        41,667             41,667
Adnan Omar..................................................        41,667             41,667
Daniel Petri................................................        41,667             41,667
Umberto Silvestri...........................................        41,667             41,667
Jonathan Solomon............................................        41,667             41,667
Dr. Lim Lek Suan............................................        41,667             41,667
Fumio Uehara................................................        41,667             41,667
Dr. Vallobh Vimolvanich.....................................        41,667             41,667
------------------------

(1) Based on ownership as of February 11, 2000. Includes shares issuable to the
    named individuals upon exercise of currently outstanding options under the
    FLAG Telecom Holdings Limited Long-Term Incentive Plan, whether or not
    presently exercisable.

                                       4
PLAN OF DISTRIBUTION

    The shares of our common stock covered by this prospectus will be sold, if
at all, by the individuals named above, and not by us. The shares may be sold
from time to time as follows:

    - on the Nasdaq National Market, in the over-the-counter market, or on a
      national securities exchange (any of which may involve crosses and block
      transactions);

    - to purchasers directly;

    - in ordinary brokerage transactions in which the broker solicits
      purchasers;

    - through underwriters, dealers and agents who may receive compensation in
      the form of underwriting discounts, concessions or commissions from a
      seller and/or the purchasers of the shares for whom they may act as agent;

    - through the writing of options on the shares;

    - through the pledge of shares as security for any loan or obligation,
      including pledges to brokers or dealers who may from time to time effect
      distributions of the shares or other interests in the shares;

    - through purchases by a broker or dealer as principal and resale by such
      broker or dealer for its own account pursuant to this prospectus;

    - through block trades in which the broker or dealer so engaged will attempt
      to sell the shares as agent or as riskless principal but may position and
      resell a portion of the block as principal to facilitate the transaction;

    - through exchange distributions in accordance with the rules of the
      applicable exchange;

    - in any combination of one or more of these methods; or

    - in any other lawful manner.

    These sales may be made at prices related to the then current market price
or otherwise at prices and on terms then prevailing, or in privately negotiated
transactions. In effecting sales, a broker or dealer engaged by an individual
using this prospectus to sell common stock may arrange for other brokers or
dealers to participate in the sale. In addition, any shares covered by this
prospectus which qualify for sale pursuant to Section 4(l) of the Securities Act
or Rules 144 or 701(g) under the Securities Act may be sold thereunder rather
than by this prospectus.

    The number of shares to be reoffered or resold by means of this prospectus
by each individual named above, and any other individual with whom he or she is
cooperating for the purpose of selling our common stock, may not exceed the
greater of, during any three-month period, (1) 1% of all outstanding shares of
our common stock, (2) the average weekly reported volume of trading in our
common stock on the Nasdaq National Market during the four weeks preceding the
date of the receipt of the order to execute the transaction by the broker or the
date of execution of the transaction directly with a market maker, or (3) the
average weekly volume of trading in our common stock reported through the
consolidated transaction reporting system contemplated by Rule 11Aa3-1 under the
Exchange Act during the four-week period specified in clause (ii) above.

    In connection with distributions of the shares or otherwise, an individual
using this prospectus to sell common stock may enter into hedging transactions
with a broker-dealer. In connection with such a transaction, a broker-dealer may
engage in short sales of shares registered hereunder in the course of hedging
the positions they assume with the seller. The seller may also sell shares short
and deliver the shares to close out such short positions. The seller may also
enter into an option or other transaction

                                       5
with a broker-dealer which requires the delivery to the broker-dealer of shares
we have registered, which the broker-dealer may resell by this prospectus.

    A seller may pay a broker-dealer or an agent compensation in the form of
commissions, discounts or concessions. The broker-dealer and any other
participating broker-dealer may be deemed to be "underwriters" within the
meaning of the Securities Act in connection with such sales and any such
commission, discount or concession may be deemed to be underwriting discounts or
commissions under the Securities Act.

    We may be required to file a supplemented prospectus in connection with any
activities involving a seller which may be deemed to be an "underwriting." In
that case, a supplement to this prospectus would contain (1) information as to
whether an underwriter selected by a seller, or any other broker-dealer, is
acting as principal or agent for the seller, (2) the compensation to be received
by an underwriter selected by a seller or any broker-dealer, for acting as
principal or agent for a seller and (3) the compensation to be received by any
other broker-dealer, in the event the compensation of such other broker-dealers
is in excess of usual and customary commissions. Any broker or dealer
participating in any distribution of the shares may be required to deliver a
copy of this prospectus, including any prospectus supplement, to any individual
who purchases any shares from or through such a broker-dealer.

    We have advised the people identified in this prospectus as potential
sellers of common stock that during any period when they may be engaged in a
distribution of the shares offered by this prospectus, they are required to
comply with Regulation M promulgated under the Exchange Act. With certain
exceptions, Regulation M precludes any seller, any affiliated purchaser and any
broker-dealer or other individual who participates in such a distribution from
bidding for or purchasing, or attempting to induce any individual to bid for or
purchase any security, that is the subject of the distribution until the entire
distribution is complete. Regulation M also prohibits any bids or purchases made
in order to stabilize the price of a security in connection with the
distribution of that security. All of these factors may affect the marketability
of our common stock.

    The people identified in this prospectus as potential sellers of common
stock offer to sell all, some or none of the shares covered by this prospectus.
Because it is possible that a significant number of shares could be sold
simultaneously by means of this prospectus, such sales, or the possibility
thereof, may have an adverse effect on the market price of our common stock.

                                INDEMNIFICATION

    Our By-Laws provide that our directors and officers and former directors and
officers shall be indemnified to the fullest extent permitted by The Companies
Act of Bermuda 1981, as amended from time to time, and provides for advances to
any indemnified director or officer of expenses in connection with actual
proceedings and claims arising out of their status as our director or officer.
We also maintain a directors' and officers' liability insurance policy on behalf
of our directors and officers.

                            VALIDITY OF COMMON STOCK

    The validity of our common shares will be passed on by Appleby, Spurling &
Kempe, Hamilton, Bermuda.

                                       6
EXPERTS

    The financial statements and schedules of FLAG Telecom Holdings Limited for
the period of incorporation to September 30, 1999 and FLAG Limited for the
period from January 1, 1999 to February 26, 1999 and for the years ended
December 31, 1998, 1997 and 1996, incorporated in this prospectus by reference
to our prospectus dated January 18, 2000, have been so incorporated in reliance
on the report of Arthur Andersen & Co., independent accountants, as indicated in
their reports with respect thereto, and are included herein in reliance on the
authority of said firm as experts in giving said reports.

                                       7
PART II
               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

    The following documents filed by us with the Securities and Exchange
Commission ("SEC") are incorporated by reference into this Registration
Statement:

        (a) Our Registration Statement on Form F-1 (Registration No. 333-94899)
    filed with the SEC on January 18, 2000, Amendment No. 1 to such Registration
    Statement, filed February 3, 2000, Amendment No. 2 to such Registration
    Statement, filed February 7, 2000, and Amendment No. 3 to such Registration
    Statement, filed February 9, 2000.

        (b) The description of our Common Stock, par value $.0006 per Share,
    contained in its Registration Statement on Form 8-A (Registration
    No. 000-29207) filed with the SEC on January 27, 2000, including any
    amendment or report filed for the purpose of updating such description.

    All reports and other documents subsequently filed by us pursuant to
Section 13(a), 13(c), 14 or 15(d) of the Exchange Act prior to the filing of a
post-effective amendment which indicates that all securities offered have been
sold or which deregisters all securities then remaining unsold shall be deemed
to be incorporated by reference in this Registration Statement and to be a part
hereof from the date of filing of such documents.

    Any statement contained herein or in a document all or a portion of which is
incorporated or deemed to be incorporated by reference herein shall be deemed to
be modified or superseded for purposes of this Registration Statement to the
extent that a statement contained herein or in any other subsequently filed
document which also is or is deemed to be incorporated by reference herein
modifies or supersedes such statement. Any such statement so modified or
superseded shall not be deemed, except as so modified or superseded, to
constitute a part of this Registration Statement.

                                    EXPERTS

    The financial statements and schedules of FLAG Telecom Holdings Limited for
the period from incorporation to September 30, 1999 and FLAG Limited for the
period from January 1, 1999 to February 26, 1999 and for the years ended
December 31, 1998, 1997 and 1996 incorporated by reference in this Registration
Statement have been audited by Arthur Andersen & Co., independent public
accountants, as indicated in their reports with respect thereto, and are
included herein in reliance the authority of said firm as experts in giving said
reports.

ITEM 4.  DESCRIPTION OF SECURITIES.

    Not Applicable.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

    Not Applicable.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

    Our By-Laws provide that our directors and officers and former directors and
officers shall be indemnified to the fullest extent permitted by The Companies
Act of Bermuda 1981, as amended from time to time, and provides for advances to
any indemnified director or officer of expenses in connection with actual
proceedings and claims arising out of their status as our director or officer.
We also maintain a directors' and officers' liability insurance policy on behalf
of our directors and officers.

                                      II-1
ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

    Not Applicable.

ITEM 8.  EXHIBITS.
EXHIBIT                 DESCRIPTION
-------                 -----------
4.1                    Memorandum of Association, incorporated by reference to
                        exhibit 3.1 to our Registration Statement on Form F-1,
                        Registration No. 333-94899, filed with the SEC on
                        January 18, 2000.

 4.2                    By-Laws of FLAG Telecom Holdings Limited, incorporated by
                        reference to exhibit 3.2 to our Registration Statement on
                        Form F-1 (Registration No. 333-94899) filed with the SEC on
                        January 18, 2000.

 4.3                    FLAG Telecom Holdings Limited Long-Term Incentive Plan,
                        incorporated by reference to exhibit 10.1 to our
                        Registration Statement on Form F-1 (Registration
                        No. 333-94899) filed with the SEC on January 18, 2000.

 5.1                    Opinion of Appleby Spurling & Kempe.

 23.1                   Consent of Arthur Andersen & Co.

 23.3                   Consent of Appleby Spurling & Kempe (included in
                        Exhibit 5.1).

 24                     Powers of Attorney (included on page II-4 of this
                        Registration Statement).
ITEM 9.  UNDERTAKINGS.

    (a) The undersigned registrant hereby undertakes:

        (1) To file, during any period in which offers or sales are being made,
    a post-effective amendment to this Registration Statement:

           (i) To include any prospectus required by Section 10(a)(3) of the
       Securities Act;

           (ii) To reflect in the Prospectus any facts or events arising after
       the effective date of this Registration Statement (or the most recent
       post-effective amendment thereof) which, individually or in the
       aggregate, represent a fundamental change in the information set forth in
       this Registration Statement; and

           (iii) To include any material information with respect to the plan of
       distribution not previously disclosed in this Registration Statement or
       any material change to such information in this Registration Statement;

PROVIDED, HOWEVER, that paragraphs (a)(1)(i) and (a)(1)(ii) do not apply if the
information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed by the registrant pursuant to
Section 13 or Section 15(d) of the Exchange Act that are incorporated by
reference in this Registration Statement.

        (2) That, for the purpose of determining any liability under the
    Securities Act, each such post-effective amendment shall be deemed to be a
    new registration statement relating to the securities offered therein, and
    the offering of such securities at that time shall be deemed to be the
    initial bona fide offering thereof.

        (3) To remove from registration by means of a post-effective amendment
    any of the securities being registered which remain unsold at the
    termination of the offering.

                                      II-2
(b) The undersigned registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to Section 15(d) of the Exchange Act) that is
incorporated by reference in the Registration Statement shall be deemed to be a
new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

    (c) Insofar as indemnification for liabilities arising under the Securities
Act may be permitted to directors, officers and controlling persons of the
registrant pursuant to the foregoing provisions, or otherwise, the registrant
has been advised that in the opinion of the SEC such indemnification is against
public policy as expressed in the Securities Act and is, therefore,
unenforceable. In the event that a claim for indemnification against such
liabilities (other than the payment by the registrant of expenses incurred or
paid by a director, officer or controlling person of the registrant in the
successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.

                                      II-3
SIGNATURES

    Pursuant to the requirements of the Securities Act of 1933, the registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of London, England, on February 16, 2000.
FLAG TELECOM HOLDINGS LIMITED

                                                       By:  /s/ STUART RUBIN
                                                            -----------------------------------------
                                                            Name: Stuart Rubin
                                                            Title: General Counsel and Assistant
                                                            Secretary
Each person whose signature appears below constitutes and appoints Andres
Bande, Edward McCormack and Stuart Rubin, and each of them, with full power to
act without the other, this person's true and lawful attorneys-in-fact and
agents, with full power of substitution and resubstitution, for him and in his
name, place and stead, in any and all capacities, to sign any and all amendments
(including post-effective amendments) to this Registration Statement and any and
all other documents and instruments incidental thereto, and to file the same,
with all exhibits thereto, and all documents in connection therewith, with the
Securities and Exchange Commission and any other regulatory authority, granting
unto said attorneys-in-fact and agents, and each of them, full power and
authority to do and perform each and every act and thing requisite and necessary
to be done, as fully to all intents and purposes as he might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents, or any of them, or his substitute, may lawfully do or cause to be done
by virtue hereof.

    Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed below by the following individuals in the
capacities and on the dates indicated.
NAME                                     TITLE                        DATE
                    ----                                     -----                        ----
/s/ ANDRES BANDE                 Chairman and Chief Executive
    ------------------------------------         Officer (Principal Executive      February 16 , 2000
                Andres Bande                     Officer)

            /s/ EDWARD MCCORMACK
    ------------------------------------       Chief Financial Officer (Principal  February 16, 2000
              Edward McCormack                   Financial Officer)

              /s/ STUART RUBIN
    ------------------------------------       General Counsel and Assistant       February 16, 2000
                Stuart Rubin                     Secretary

           /s/ MICHAEL FITZPATRICK
    ------------------------------------       Director                            February 16, 2000
             Michael Fitzpatrick

            /s/ EDWARD J. MCQUAID
    ------------------------------------       Director                            February 16, 2000
              Edward J. McQuaid

               /s/ ADNAN OMAR
    ------------------------------------       Director                            February 16, 2000
                 Adnan Omar

              /s/ DANIEL PETRI
    ------------------------------------       Director                            February 16, 2000
                Daniel Petri
II-4
/s/ PHILIP SESKIN
    ------------------------------------       Director                            February 16, 2000
                Philip Seskin

            /s/ UMBERTO SILVESTRI
    ------------------------------------       Director                            February 16, 2000
              Umberto Silvestri

            /s/ JONATHAN SOLOMON
    ------------------------------------       Director                            February 16, 2000
              Jonathan Solomon

         /s/ DR. VALLOBH VIMOLVANICH
    ------------------------------------       Director                            February 16, 2000
           Dr. Vallobh Vimolvanich

             /s/ LARRY BAUTISTA
    ------------------------------------       Authorized US Representative        February 16, 2000
               Larry Bautista
II-5
EXHIBIT INDEX
EXHIBIT                 DESCRIPTION
-------                 -----------
4.1                    Memorandum of Association, incorporated by reference to
                        exhibit 3.1 to our Registration Statement on Form F-1
                        (Registration No. 333-94899) filed with the SEC on
                        January 18, 2000.

 4.2                    By-Laws of FLAG Telecom Holdings Limited, incorporated by
                        reference to exhibit 3.2 to our Registration Statement on
                        Form F-1 (Registration No. 333-94899) filed with the SEC on
                        January 18, 2000.

 4.3                    FLAG Telecom Holdings Limited Long-Term Incentive Plan,
                        incorporated by reference to exhibit 10.1 to our
                        Registration Statement on Form F-1 (Registration
                        No. 333-94899) filed with the SEC on January 18, 2000.

 5.1                    Opinion of Appleby Spurling & Kempe.

 23.1                   Consent of Arthur Andersen & Co.

 23.3                   Consent of Appleby Spurling & Kempe (included in
                        Exhibit 5.1).

 24                     Powers of Attorney (included on page II-4 of this
                        Registration Statement).