1976 - 1982.
EDIT: 43002 - 055 were initially Western Region power cars operating between London, Bristol & South Wales and these were introduced between February 1976 and June 1977 allocated to PM and OO. After this build came 43056 - 43119 between June 1977 and April 1979 for the full Scottish HSt service to be introduced the following month, but this was delayed due to Penmansheil Tunnel Collapsing - these were allocated to BN, NL, HT and EC depots. 43120 - 123 were initially spare power cars, but they operated on the Eastern Region. 43124 - 152 were allocated to OO and PM depots being delivered between April 1979 and June 1981. Laira depot received it's first allocation of HSTs in 1981, starting with 43163 to 43198 in August 1982.
Depot codes:
OO Old Oak Common
PM St Philips Marsh
BN Bounds Green
NL Neville Hill
HT Newcastle Heaton
EC Edinburgh Craigentinny
LA Laira