I’ll start the walk outside Blackwells cafe, 10 The Common, Chipperfield, WD4 9BS

Grid Reference: 045015 on the following maps 1:25,000 - 182 (St. Albans and Hatfield) but if you want to follow the walk around 172 (Chiltern Hills East) would also be useful. 

I would recommend bringing food for lunch although there will probably be the option of a short pub stop. The walk will take in bits of the Chess Valley and Church End + Sarratt, but the Cock Inn, Church End & Saratt pubs are about two thirds/three quarters of the way round.