The Mills (and most of the other buildings) at Maen Offeren are already listed buildings!
Aha!
Well, that makes life a bit more interesting: that at least means that the buildings can't be demolished without permission and presumably de-listing, which I can't see happening as there would be no justifiable reason for doing so.
AFAIK, there are relatively limited powers to force the upkeep of the buildings in a decent state, although at the moment the mills could probably do with a few days' TLC in order to keep the worst of the weather (and vandals) out.
Sadly, many owners have an attitude towards listed buildings in that they allow them to decay to such a state that they are unsafe or beyond repair. Indeed, in Glasgow, listed buildings have a habit of "going" on fire.
I wonder how concerned Greaves are about their listed buildings?
Hello again darkness, my old friend...