House in multiple occupation: How many tenants trigger the requirement for a mandatory HMO licence?

A mandatory HMO licence is required in England and Wales for renting out a large HMO which is a property rented out to 5 or more people who form more than 1 household with shared toilet, bathroom or kitchen facilities and where at least 1 tenant pays rent.  

A threshold of more than 6 tenants is relevant to the application of planning law to HMO use.  Permitted development rights apply to a change of use from Class C3 (dwellinghouse) to Class C4 (HMO) unless the local authority has removed them by means of an Article 4 direction.  A C4 HMO is a small HMO in planning law.  In planning terms, a large HMO is one that is used for more than 6 persons and a large HMO is sui generis and always requires planning consent for a change of use from a dwellinghouse.  Also bear in mind that the development works to redevelop the property to an HMO may require planning consent.

So numbers matter for HMOs, both for the HMO licensing regime and for the application of planning law.  As you can see, the requirements are different and a property may require a mandatory HMO licence but not planning consent.