A small number of councils have supplied information about places where they allow overnight camping in car parks. The list available from link: HERE
I am not that computer literate, but Graham Hadfield has contacted just about every council going and has a web site. I will look at it and come back
It's all in the sig The site has answers from every council responsible for car parks in England, Scotland & Wales. The situation is a bit different in Northern Ireland but I did get what information was available. Also input from National Park Authorities and some other organisations. Just as important, contributions from users of the site who have been kind enough to send in their experiences - good or bad. Graham