Well, I'm not UK (US), but my Arrow is marked "not for road use" among other things. This is on the inside of the pipe, against the bike. Its etched in, and I had to enhance the photos to make it show up. Its there, but on the bike it would be impossible to see unless you knew it was there. You'd have to crawl under the bike and stick your head between the rear suspension link and the tire from the opposite side to see it, and only if the pipe was clean.
And to head off the questions about the dent, this is a leftover from being rearended, bike's fixed, I just use the spare can for track days.