The UK's Finest Independent Forum for Shooters and Gun Owners. Est 2010.

Initially I would say illegal and S5 however:

Section 5 (1) (1.2) any firearm which either has a barrel less than 30cm in length or is less than 60cm in length overall, other than an air weapon, a muzzle-loading gun or a firearm designed as signalling apparatus.

So it may well be deemed to be legal as a muzzle loading firearm however the important this to remember regardless of category is it is a firearm.

This is certainly not an area I know anything about so hopefully someone can take a better view on the legality of owning such a thing.