There are exemptions to the rule sof what can be an HMO by the 2004 Housing Act specifications.

These are described under Section 14 of the Housing Act 2004

This list properties that are NOT HMOs

These are Buildings:

Controlled or managed by public sector bodies (local authorities, housing associations, police, fire and health authorities. etc)

Occupied by students and let by the educational authority establishment where they are studying

Occupied by religious communities for prayer, contemplation, education or the relief of suffering

Occupied by owners (An owner is someone with the freehold, or a leasehold for more than 21 years, or a member of their household

Occupied by two people (even of they form two households)