The reason that I ask is that I have a U.K. deactivated No4 mk2 with the normal U.K. military markings etc that would be expected but it is the only No4 rifle that I have seen with a butt disc. This butt disc is made of plastic but appears professionally fitted by inletting it into the butt and it has a number marked on it, presumably a rack/armoury number. I will try to post some pictures later when I get time, perhaps at the end of the week. This deac is quite precious to me because it was the first one that I purchased and it is a fully matching numbers rifle apart from the mag; even the wood is number matching. It doesn't appear to have had too much heavy use, it's just used.