I dunno about UK but at "my" construction site there is a company that only does "Kernbohrungen", large diameter drillings. Probably not cheap to only to get them to do a single hole though... Otherwise some tool rental company could have the goods? You have boels in the UK?
Oh I could do it. Just rather find a better solution before banging a hole in a beautiful old stone wall and having a vent on the outside. We're not talking bricks but granite stone.
I'll go up into the loft and then hide it behind a false wall up there.
Yeah it's possible but a bitch. Stone walls, rendered /mortar on outside but 'mud mortar' inside.
Thanks for tip on extractor. I might go without and retrofit if needed. Or fit in conjunction when doing the second bathroom in room next door.