If it has to be near London then why not true the beautiful and historic Epping Forest in Essex, often regarded as one of the finest ancient medieval woodlands in the country. Its amazing how wild the forest is considering you are no real distance from London. I found this campsite link ->
http://www.ukcampsite.co.uk/sites/re...asp?revid=1384
Im sure there must be other campsites in the area
