DaveF
Hi
Thanks for that.
"The lane is one way coming from Commercial Street (by White Heart). There is a red/white no entry sign on a lamp post"
OK, got that.

However I'm still confused by the Gurney Mews stretch. 
https://www.openstreetmap.org/way/37327795

Is it accessible by motor vehicles?
Is it two-way? 
If not, can vehicles head South along it, exiting into Cross St.?