How do guns end up in the hands of criminals?

How do guns end up in the hands of criminals?

Criminals get guns usually illegally because they're criminals. And certainly that's the case in England because there are no legal handguns in England, other than a few owned by the police. Even the British Olympic team has to go to Belgium to practice, and yet the police figure there are twice as many illegal guns in that country as when they confiscated them. So the more they confiscate, the more the criminals have guns. Doesn't seem like a good idea to me.