How laws allow old US guns into the hands of UK criminals

In the US any gun made prior to 1899 is classified as an antique.

In the UK a gun has to made before 1939 and take ammunition on the Home Office’s obsolete calibre list.

Dozens of types of revolver currently meet this criteria, making them exempt from the need for a Firearms Certificate. The only restriction is that people who have served at least three months in prison cannot own one.