risk assessment's sounds a good idea but with cash strapped councils like ours and the time to do such things may be you have allotments that do have H&S issues but I have to say we have more problems with letting the plots than H&S issues
we also have regular visits from the council allotments rep that keeps a eye on things although we mite be attacked by snakes coming out of the uncultivated allotments that have been let to would be allotment holders that we never see