Brad
PS&S Ltd - Prince-Smith & Stells, Keighley,Yorkshire England- they were assemblers of the bayonet using components supplied by other companies. They delivered 1,067,039 No 4 MkII* bayonets.
J.W.(S) Ltd - John Wilson Ltd of Sheffield, Yorkshire - responsible for forging the socket.
T.R.M.1 - thought to be a sub-contractor used by Wilson (+ others).
Hope this helps - the information is from "Spirit of the pike - British socket bayonets of the Twentieth Century"" by Graham Priest
Regards
Richie