When a government starts an across-the-board prohibition on something desireable, the one thing you can count on is a thriving local black market for the prohibited good or service.
If you are really bent on breaking laws, you'll likely find local procurement to be easier. Breaking US purchase laws, getting through US airline security (sure it's a joke, but even blind dogs get a bone now & again) and clearing customs in the UK... You're asking for more problems than you need.
Another thought..... expecting to be able to effectively engage a bad(er) guy with a weapon you cannot practice with... not a good idea. I'd recommend somthing a little simpler, like an ASP Palm Defender keychain.