mabey it is ok to stay a night if there's not that many about , i have stayed many a time on car parks that have had these no camping /sleeping notices up all over and never been told by anybody to move .i suppose its when you get a dozen or so vans parked up people start asking questions . my rule of thumb was always if its quiet and largely unoccupied then i will stay one night , but if its busy there's always something a little further on . ive found there is little in the way of authority around at night except the cops and there largely too busy with other things to worry about a camper van parked up out of the way in a darkened corner . its the ones that decide it would be a good idea to spend a weeks holls in one place that are the bug bear .