harg
The footway doesn't seem to be marked at http://www.hertfordshire.gov.uk/services/envplan/countrysideaccess/row/defmap/DMwebmap/ 

I wonder if you are thinking of FP58 which crosses the M25, is mentioned at http://www.ifootpath.com/display-ifootpath-walk?walkID=2833 and is currently unmapped -- but that is about 1000 metres away from the marker.


