Don't forget that any registered one can be changed to electric, which saves all the hassle of SVA.
Interestingly, I saw a vintage moped on the road today. I couldn't get a close look, but it had a black and white rear number plate and a step-through frame. It looks like it could be a Velo-Solex. there's definitely something over the front wheel. it's a shame that car overtook it at the beginning of the vid. Today is full of coincidences like that! I was on my road bike and gave chase. I got close after taking a short-cut round the roundabout, but that car didn't indicate, so I had to slow down before crossing the last bit, then I ran out of puff when the road went uphill. The moped was doing about 20 - 25 mph. It's much clearer in the original 4k. What do you think Velo-Solex or not?