What is the car in this 1959 Pathe clip about DIY catamarans?

[GrahamM376]

Originally the regulations were very restrictive: small engine, lightweight and no reverse gear , which traditionally caused fun when the proud owners drove their new Isetta home and right up to the back of the garage. Later on things were more relaxed, and it was basically a just a weight restriction at something like 1000lbs empty. Reliant three-wheelers (Regal, Robin, Rialto) came under that rule.

In 1962 (when I got my first Morgan) to drive at 16 on a motorbike license it had to have the reverse gear blocked off and weight unladen had to be under 8 cwt = around 400 kg. Don't know if there was any power restriction, there wasn't for motorbikes, but the Morgan was 990cc.