Piddletrenthide straddles the B3143 which is reached from Puddletown on the A35. It is about 7 miles north of Dorchester. It can also be reached from the north via Sherborne on the A352. On a good day it takes about 2 hours from the M25.
By Train:
There are direct trains from Waterloo to Dorchester (journey time about 2h 30m) and also to Sherborne (journey time about 2h 15m). Taxis from Dorchester South station should cost about £15.