IMPORTANT WARNING!!!!!
DON'T BELIEVE EVERYTHING YOU READ ON PEPIPOO!!!!!!
If there were clearly displayed signs, making it clear that you'd be charged for exceeding a certain length of stay, you entered into a legally binding contract by parking there. The company responsible for controlling car parking at that supermarket have every right to enforce that contract.
If you don't pay up, things could become very expensive!
See here:
http://www.rochdaleonline.co.uk/news-features/ 2/community-news/15278/judge-enforces-parking- penalty-in-landmark-case
Chris