HMO Housing falls under C4 of the Use Class Act i.e. Houses in multiple occupation, which is defined as small shared houses occupied between three and six unrelated individuals, as their only or main residence, who share basic amenities such as a kitchen or bathroom. Certain councils need planning approval where article 4 is in operation. Salford, Manchester, Birmingham and Leeds councils require one of these, but Bolton and Liverpool councils don’t. Therefore you do not need planning permission to convert a Use Class C3 (Family Dwelling) to become Use Class C4 if Article 4 is not in operation. However if you want to convert a house into a HMO with more than 6 beds then this falls under the Sui Generis Use Class which will require planning permission.