UKcampsite is a useful source of free information and advice through the internet. The others are commercial enterprises with there own network of expensive but quality assured campsites.
There are many other independent and quality camp sites available and it is not necessary to join the caravan club or camping and caravanning club.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.