Are you stupid enough to actually believe this? My uncle was put in prison for over a decade for robbing banks in the UK. He slept with a shotgun under his pillow (the police found it there when they arrested him).
Believe it or not criminals do have guns in the UK (police confiscate guns all the time), as well as as other weapons which are illegal (swords, machetes, nun-jucks). Recently police raided a warehouse (near where I live) where they were making firearms.
Also I am pretty sure guns were illegal in Northern Ireland as well and plenty of terrorists and criminals had them at the time.
It really annoys me when people try to claim the opposite (or gaslight me) by saying "well they banned all the guns that means that there isn't any" because I know it isn't true.