After a two year battle trying to use common land (!) and parks, in 2012 I presented a full report the to national parks along with insurance, qualifications, experience, and written support from nearby landowners, users, etc. and eventually received a two page written reply stating why it was deemed inappropriate use of the land. I'd had enough by then (and also met others who encountered similar problems) so just found better places to use. Don't know about the intricacies of the law but I wasn't prepared to drag it out any further.