New No.1 Mk4 owner

[Surpmil]

It's a Maltby and looks to be dated 1942. I have doubts about the SN as it is a restrike of one of that appears party illegible. It could be the number began "BY----", but what may be a heavier restrike of the Maltby "M" was mistaken for an "H". You can see there is most of what is either an "8" or a "B" ahead of the "Y" in the upper serial number. "8Y---" would not fit the sequence I believe so it must be "BY----"

The bolt is obviously a mismatch, the barrel was replaced with one dated 1945. It's London Proof House marked and if that is a D in a circle on top of the Nock's Form (barrel flat over chamber) then Skennerton gives that a "draw-lapped barrel", which someone will have to explain!

There's a small circular mark on the barrel ring I cannot ID either.