In this guide
3. Build an extension to a ground-floor flat
To add an extension to your flat you must apply for planning permission.
If your flat is a listed building it is likely you will need listed building consent and you should contact your local planning authority for advice before you start work.
Works to a listed building that affect its special historic character without consent is a criminal offence.
If your flat is in a conservation area and your proposals involve an element of demolition then you may need to apply for conservation area consent and you should contact your local planning authority for advice.