BSA Commercial No1 Mk3.

[lawrence_n]

That is an interesting rifle - the BSA logo on the barrel, the sale permit mark, the varnish finish and the 320B inspection marks all suggest a commercial sale for target use, yet it has a letter prefix and military inspection marks.
Maybe a commercial rifle using up now surplus military production after the war?
As Bindi requested the markings on the butt socket and also has the barrel a square cut muzzle would be of great interest - also any commercial proof markings?

Alas, the rifle is currently out of my hands. When I get back up north, I'll take the snaps you've requested but it'll be a while.