And it would be regulated as a firearm in the UK ("a lethal barrelled weapon of any description from which any shot, bullet or other missile can be discharged";

And it would be regulated as a firearm in the UK ("a lethal barrelled weapon of any description from which any shot, bullet or other missile can be discharged"; section 57 (1) Firearms Act 1968). There is also a specific list of prohibited weapons in the same act which are firearms even if non-lethal.