i hate to be the guy that is pissing in the beer mug, but to me that looks like it never saw england.
The square brigde is sweated on(not part of the forging) so it is not a single square brigde mauser, and i never saw base's like that on a london gun with allan head screws.
the engraving is the most telling sign of a gun out of pakistan or afganistan in the mid range, nicely looking but way to crude to be from any london shop.

again i might be wrong.

please show the proof marks and the writing on the barrel, that should give an indication.

best regards

peter