The liability to pay council tax is determined by the hierarchy of liability as contained in s.6 Local Government Finance Act 1992. Basically you start at the top of a list of liable persons starting with owner-occupiers and work downwards until the appropriate person is found and that becomes the liable person.
However, under the Council Tax (Liability for Owners) Regulations 1992, an owner will always be liable if the dwelling is an HMO. The definition of an HMO for council tax purposes is totally different to that contained in the Housing Act 2004. For council tax purposes an HMO is defined as:
a dwelling which
(a) was originally constructed or subsequently adapted for occupation by persons who do not constitute a single household; or
(b) is inhabited by a person who, or by two or more persons each of whom either—
(i) is a tenant of, or has a licence to occupy, part only of the dwelling; or
(ii) has a licence to occupy, but is not liable (whether alone or jointly with other persons) to pay rent or a licence fee in respect of, the dwelling as a whole.
The landlord owned a house which she let on a series of assured shorthold tenancies between 1999 and 2007. In 1999, the tenancy was granted to four tenants on a joint and several basis. When one tenant vacated, the dwelling was let to the remaining three tenants, again on a joint and several basis.
When the tenants originally moved in, in 1999, they agreed with the landlord that because they did not require the use of the furniture supplied, it would be stored in the conservatory at the rear. They also agreed that they did not require use of the conservatory.
Despite the tenancy(ies) having one rent shown for the whole house, the tenants paid the landlord their share of the rent individually, which continued until 2008 when the tenants vacated.
The local authority had billed the tenants for council tax from 1999 until they vacated but then subsequently decided the property was an HMO and therefore billed the landlord the sum of around £11,000. The landlord appealed to the valuation tribunal. The tribunal agreed with the local authority that the property was an HMO because (a) the tenants each paid there share of the rent and (b) the tenants only rented part of the dwelling because of the lack of access to the conservatory.
The landlord successfully appealed to the High Court.
Although the tenants had each paid a “share” of the rent, this had been an arrangement of convenience commonly found in shared properties. Under the terms of the tenancy agreement, they were jointly and severable liable for the rent. The fact that they had paid separately did not change their legal liability. Nor was the tenancy only of part of the house. The tenants were clearly entitled to use both the furniture and the conservatory, even if they had chosen not to do so. Accordingly, they were not excluded from any part of the property but had merely voluntarily decided not to use one part of it.
The judgment is available here.
Additional footnote: this same principle has also been applied in Shah v Croydon LBC  EWHC 3657 (Admin) where a landlord appealed a Magistrates Court decision to hold him liable for council tax where there were two tenants sharing:
you would expect in any case in which there is more than one tenant in a property (if those tenants are not either married or partners occupying the same room) that the tenants would be sleeping in separate bedrooms. Perhaps they would also be sharing the communal areas, but as the case of Goremsandu makes very clear this sharing (in and of itself) does not mean that they are not entitled to occupancy of the house as a whole. What matters is what they are legally entitled to in exchange for the payments of rent they are making to the landlord.
Although in this case, the landlord was fortunate and the tenants held liable, it was clearly a close call and could have gone either way. It is the tenancy agreement that matters.
A landlord should be careful if any part of the building is excluded from a letting such as a loft, storage space or joined garage because this could be seen as the letting of part of the building and as a result the landlord would be liable for the council tax.