As far as I can see a DZ is an area where permission has been granted to drop parachutists, it is not controlled, restricted, prohibited or protected for this purpose at all. The parachutist and the pilot have equal right to be there, however the Caa advise that pilots do not fly through unless they can be sure it is cold. It could be a very unfortunate mistake for parachutists to believe they have any overriding right to exclusive use of a DZ.