The proof marks on the barrels of your gun are those of the Birmingham Proof House, circa 1954-1994. They are for a 12.G gun with 2.5 inch chambers. Allowable bore size for 12g is .729/.739 inches. Provided the chambers still measure 2.5 inches your gun is in proof.
The action bears a London view stamp[V surmounted by a crown] and some indistinct marks that look like Birmingham proof marks. This suggests to me, that your gun was origionally proof tested in London and rebarrelled and re proofed in Birmingham.
