Client rents out a self contained unit in their garden via Air BnB. About 20 lets a year totalling 80 nights a year.
On the one hand I have read that self contained units do not qualify for rent a room but I can't see that in HMRCs guidance.
HMRC 223 (2019) says you can use rent a room if letting activity amounts to a trade like a guest house or a BnB. I can't see why this Air BnB should not qualify as a trade.
The only thing though is that further down in HMRC 223 it says you cannot claim rent a room if it is not part of your main home. However is some-one's garden not part of their home? When I sell my home the garden will be included.
Is "part of your home" defined more precisely anywhere or should the client claim the rent a room on the basis that it is a trade conducted from their home which to me includes their garden