While I fully understand that remaining indefinitely at York Street is a non-starter, I do not believe that the Council, or any other body, can force a change of use of existing premises, except for compulsory purchase for an over-riding reason. It can only interfere on change of use. Only the owner (or potential purchaser) may apply for planning permission for change of use, but would not need to apply for continued use in the same way.
It is obvious, however, that the present owner is not going to miss a golden opportunity to make a killing.