The first place in the UK that actually has the ability, the reason and money to go to 100% non fossil fuel vehicles within say 5 years are each of the Channel Islands.
However let me guess where the last place will be
You could argue that Sark already has,
being 2sq miles in land area cars are not allowed, tractors are if you need them for moving large objects but otherwise it's foot or pedal power.
Herm, the largest vehicle allowed at all is a quad bike.
My guess is that cars are allowed on Alderny is similar to Guernsey, Convenient, able to transport your stuff about etc, if you imagine every movement you make around your city (except most of the area is rural / rural town) there are only a few of us on here who could cope without a car. I know I couldn't due to some of the odd stuff I take to places. Many people probably have a car because of those times they will need it and then use it more often because it's convenient / it's there.
I've biked round most of Guernsey, life there without a car is easy enough, but as most car hire places there are aimed at tourists, the moment you need a car for the weekend, it's expensive and needs to be booked long in advance.