Which factory made this No. 4 Mk I?

[Roger Payne]

Going back to the original question, it's definitely a BSA Shirley. BSA initially marked their rifles with a 'B' (1941 till some point in 1943), then they commenced using the foctory coding in 1943, but for a short while only used M47, before adopting the full M47/C from later in 1943 till the end of production.

ATB