Generally changing the use of a dwelling house (C3) into a small house in multiple occupation (C4 use class) is classed as permitted development, meaning that HMO planning permission is not normally required, subject to certain limits and conditions, although please see below for restrictions to this.
In addition, it is generally classed as permitted development to change from a C4 Use (small houses in multiple occupation) back to a C3 (dwellinghouse) without the need for planning approval. Please note that while planning consent may not be required, other approvals and licenses, such as Building Regulations approval may also be required.
If you are looking to convert to or from a House in Multiple Occupation, contact us to discuss how we can assist.