The history would seem to include having the three holes for the rear pad filled in with weld. Presumably the front holes as well, but that's not clear from the photo. Whoever did it could have at least found a MkI cocking piece for the poor old thing.
The linished butt socket usually indicates some time in India's sunny clime, so perhaps it was stripped of the pads out there and some enterprising soul in the UKthought to "improve" things by filling in the holes and hot-tank bluing it.
We all see the modified non-original backsight, magazine etc. Would have been better off with a coat of Suncorite IMHO.