Handguns, or most of them, have been illegal on the UK mainland since 1997. They are perfectly legal in NI and in the Isle of Man. Handguns up to and inc .22 are legal, as are some other kinds. Most UK guns are and have always been rifles and shotguns. Handguns really only started being popular in the 80s due to US TV and film, the Dirty Harry films etc.
At my local gun club, I was surprised to learn .44 calibre black powder revolvers were still legal but single shot .22 calibre pistols were not. The former shoots a big, hefty bullet too that could send a man flying to the other side of the room. Just shows how ridiculous and ill thought out our gun laws are. They don’t even make sense.