Small steps Howard - start with the simple, build some momentum and trust from the authorities, and move on from there. A lot of other people do it.
Basic risk assessment and go under the umbrella of another group for some public liability insurance
WCCPS, WHPS and a lot of other people do them all the time so it isn't difficult
Still why does it need a formal group. Get a group of people together buy (or beg) for a couple of hippobags and tidy to their hearts content
I am sure if DDC moan then run to the press and get some publicity (or more likely some letters moaning about red tape and the council and no-one joins in to help!!)