Last I heard (many years ago) was house was off the market, council would
not give retrospective planning permission as back door was through garage
(something like that) and a charge was being made against the property
(what ever that is) by the council as they were going to demolish/fix the
problem.

If the council issue an enforcement notice requiring the owner to demolish
and it is not complied with then the council can, with a court order, do the
job themselves and bill the owner for the cost of doing so. They can also
place a legal "charge" on the property that will prevent it being sold until
the money is paid, with interest added as well. It is about to happen
locally to a couple who built a bungalow without permission and have taken
repeated court action to try and prevent the inevitable. So far the local
council tax payers have had to foot the bill to the tune of some £150,000.