In itself I'm not greatly concerned about this, our only real concern was
being left open to any potential action in the future (it's a G11 listed
building as well, so there is the issue of listed building consent of
course, but AFAIK, the work predates that anyway, so should isn't an
issue)


If the building is listed then there is no time limit as far as enforcement
is concerned. Even if unauthorised work was done by a previous owner the
current owner can be forced to undo it at his cost. Also remember doing any
unauthrised work to a listed building is a criminal offence as well.

Peter Crosland