Old gun re- barrelled , Birmingham proof . I would suggest that at the time the work was done, a lot of people did not bother which Proof House it was sent to so it could have been done in Birmingham or by some one out side in the so called provinces.
As it appears to be a non ejector it would not have been worth sending back to the makers [Purdey]and had it been so they would have marked the barrels as having been made by Purdey of which I have seen several examples .