A couple of years ago we went to England on vacation. I too noticed alot of scooters and small motorcycles. I will say this. The roads there are extremely narrow.. Traffic is horendous. I'm sure that driving a scooter is much more praticle then a car there. Also, that year they started charging a "toll" for anybody riding "into" London. Because of the traffic, they were pushing hard for using the transit system, of which I must say was/is awsome. You can get anywheres on there underground rail system. Easy and cheap.
To give you an idea of how narrow there lanes are, all the trucks, busses and most cars have there side view mirrors mounted in front, not sticking out the sides like on our cars. If they were sticking out the sides, they'd get clipped off right quickly.