Use Classes and Change of Use
Planning laws classify uses of land and buildings into various categories called Use Classes. A Use Class is a grouping together of similar land uses. For example, shops are grouped as Class A1, restaurants and cafés as A3.
Planning Portal Guidance on Change of Use. Changes of use within the same Use Class do not normally require planning permission; for example, changing a shop from a butcher to a chemist (both Class A1).
Some changes of use between different Use Classes are permitted by the Town and Country Planning (General Permitted Development) Order 1995. For example, a bank (Class A2) to a retail use (Class A1). The Planning Portal provides a list of Permitted Changes. All other changes of use are likely to require planning permission.
Certain unique or unusual uses, for example, nightclubs, do not fall within any Use Class. These uses are called 'sui generis' (of their own kind). Planning permission is likely to be required for any change to a 'sui generis' use.
Please remember that although the Use Class Order may permit the change of use of a building, planning permission may still be required for associated building works.
Also, the current or previous use of a building does not mean that those or similar uses are lawful, so check with Development Control that your proposal is acceptable.
The following local Policies will help you to understand the context:
If you require a formal confirmation of the lawful use of land or premises you will need to contact Development Control for a planning history or to apply for a Certificate of Lawful Use. [Brighton & Hove LDC Checklist]