In particular with the introduction of licencing, the size of bedrooms can matter. Sometimes a local authority can limit the number of occupiers depending on the room sizes or in rare cases can state a room is not suitable for occupation at all.
It should be noted that the minimum standards for a licensable HMO (contained in Schedule 3 of the Licensing and Management of Houses in Multiple Occupation and Other Houses (Miscellaneous Provisions) (England) Regulations 2006) makes no provision whatsoever regarding minimum room sizes.
I have been unable at the time of amending this article to find any Residential Property Tribunal decisions that relate to minimum room sizes.
Housing Act 1985
The legal standards covering overcrowding are contained in the Housing Act 1985 and cover all dwellings.
The occupancy level standards for dwellings are laid down in Part X of the 1985 Housing Act, which specifies maximum permitted occupancy levels in consideration of the total number of habitable rooms available and the number of persons liable to be occupying individual rooms for sleeping purposes.