It's probably a genuine enough 4T but as husk says, more photo's with greater detail of the markings, areas showing the body pads (with scope & bracket removed) would be helpful. It has clearly been rescoped (& rebracketed) as the Mk3 scope did not go in to production until October 1944, & the bracket bears the serial of a 1944 BSA produced rifle. It's a question of who & when did the rematching. If the G31222 is not barred out then it is likely the scope & bracket have been put on by a civvy. However, we shouldn't say too much without some more revealing pics....!