You have a standard Lend-Lease British Service model from mid-1943.
The absence of British post-war commercial proofs indicates that it somehow made its way out of British or other Commonwealth service and back here through channels other than being regularly surplused out in Britain.
The CAL .38 SPECIAL marking on the left frame is not seen often on converted guns, and assumed to be the peculiarity of one particular converter, although we don't know who. It does indicate that however your gun got back here, it entered the commercial surplus trade at some point.
Most of these came back before 1968, so no import marks are usually found.