Just learned from Clive Elliott that 10-cwt trailers were not only used during WW2 but soldiered on until the 1950s-60s. EMERs (Electrical and Mechanical Engineering Regulations) continued to be issued into the mid 1960s.
This is what the "Trailer, 1/2 Ton, 4.2in, Mortar Ammunition No.1, 2 Wheeled" looked like in the 1960 parts list:
