I've found exactly the same problem with hammocking at "proper" campsites. I got the same feedback about garoting etc, and also about not being allowed to tie anything onto trees, as apparently this would harm them.
Ironically I have hammocked at a large service station just outside of Frankfurt, between a tree and a lamp post in the parking area. The German police had a look at me setting up, and then left me to it. I also got a lot of strange looks from the caravan dwellers. :yelrotflm
I sometimes find the time to go surfing in North Devon, and would ideally stay on a campsite with washing facilities (hot showers!) and sleep in my hammock (so much more comfortable). If anyone knows of anywhere around Croyde, please PM me, or reply on here.