I used to work on Watling Street, just north of Radlett.
The industrial estate there is on the site of the Handley Page factory, where Victor bombers were built.
On the left of the road opposite XMA, look for an old looking building. The lady there used to run a craft shop.
She showed me round the house, and showed an old inn sign for Ithink the George and Dragon. this house was a very old inn,
a stop on the road out of London.
As an aside, that GPX route follows Watling Street. Why is there a kink around Elstree? Do the modern roads not reflect Watling Street at that point?