Thanks for the replies.
Someone near me has applied to change (I think) c2 to c3, which will be individual rooms in a shared house. I didn't think it had been decided yet but it seems they are already letting them out - I was wondering if that meant they have had the permission granted or if...
If someone has applied for planning permission for a hmo but this has not yet been approved, what are the rules on letting out the property in the meantime? Thanks for any advice.