Selling a Static Caravan 31 July 2020 at 3:28PM in UK holidays, days out & entertainments

LA85

Trying to help some friends out. They wish to sell their static caravan, but have been told by the site owner that in order to do this, they have to empty it at the point they wish it to go on sale, and are not allowed to use/enter the caravan again. Is this legal? They have recently paid £4000 in fees, which they have been told are not refundable, but it seems harsh that they cannot use it while it is on sale. Any advice?