The law in the UK, covered a billion times in other threads, allows you to use reasonable force in the circumstances. So if you're attacked with a paperclip, you fight back with a paperclip. If you are attacked by a knife, you defend yourself with a knife. If you're attacked by a gun, you unlock yours and fight back with with a gun. Does that sound logical?
In America, someone fights you with a paperclip, and everyone whoops and slaps hands because you went straight for your gun and shot off 40 rounds.