BSA had the only factory making rifles in Britain at the start of WWII. They established a lot more factories making a lot of different weapons and equipment in the course of the war. Two that I know of producing Lee Enfield rifles in Birmingham were that first one at Small Heath and another at Shirley. I know the Shirley factory eventually made No.5s, and as a new factory I would guess it started out making No.4s. Small Heath may have started the war making No.1s and would have switched to No.4s. Of the 1,250,000 rifles sunray mentioned I would guess No.4 production would probably account for around a million of them.