It's off a BSA 1943 rifle, AV prefix, probably latter part of 1943. The serials are usually four digits after the two letter prefix, but I guess that's because there are a lot more four digit options available. You have to start at AV 1 & work up, I suppose.......
That's a very astute observation Rob! It would be nice if we could confirm that scope & bracket have been together since picked up in 1944. The font of the serial number marking is certainly what is commonly encountered but which we have usually attributed to being a post WW2 feature........