Sure it does. Nobody is supposed to have handguns in England, right? They were banned, weren't they? So what was this criminal doing with one?
Let's take your example one step further. Let's say the perp attacked the guard with a baseball bat. The guard, in fear for his life, snatches the bat and hits the perp over the head killing him.
Except for the nutty laws, I can't see how the guard could go to jail in either case. COMMON SENSE would dictate that he should not. Now, if the guard had his own ballbat and snuck up on the perp and popped him one, now your talking!