I just returned from hols in Norfolk, and driving along the coast road between Hunstanton and Wells Next the Sea, came across a camp site in Burnham Deepdale which has teepi's for hire (pricey though, about £90 a night) they are fully kitted out, even having a woodburning stove in. Seems like a great idea though, so I am sure they would be cool about you bringing your own!
------------- its me again!
Top End Farm May
RSPB Big Camp June
Diamond Campsite August