I believe there's a good commercial campsite at Salcombe Regis. Designed for caravans, but that type of site is usually very nice for pitching tents, with flat ground and services that work.

Recommended (if I've got the location right) by a friend who takes his family and doesn't want to rough it in the crowded festival site.

Sorry can't remember the name. I'm sure Google will help.

Anahata