Weren't they originally used by ex motorcycle riders (who tended in the past to be DIY) as if reverse was blanked off they could drive on a full motorcycle license.
As an apprentice I recall there was a lad in the village who had the pi** taken out of him, for driving his restricted three wheeler into his tight garage and then being stuck as he couldn't open the doors or reverse out.
There were some strange driving regulations in those days. I had a 125cc Lambretta series one as my first "ride to work" vehicle, but was able to sell it and ride a 600cc Matchless G11 Super Clubman motorcycle complete with sidecar on L plates and take passengers, it was great fun for a 16 year old and spent a lot of it's time on two wheels, especially with my hard cornering, happy days.