I beg to differ.
a) Of course all arrangements can create a liability. But I doubt it was the intention of the parties to create a legally enforceable contract. I doubt there is even a verbal agreement that would stand up.
b) being asked for money does not make it rent or create a liability! If you go round to your friends house to watch the football, hand over twenty quid for the drinks etc and fall asleep until the morning ….! The mind boggles.
c) there is a lot of discussion about “permisson to occupy” e.g. whether a person has the right to do so as a landlord if they are a tenant themselves or the property is mortgaged.
Finally, what EXACTLY is the RO supposed to value if they turn up to inspect? A living room avalable between what hours? A non-exclusive space on the floor?