Not all developments need planning permission. You do not need it for some types of small development, known as permitted development. Planning Portal has guidance on common types of projects and whether they need planning permission.
Some permitted development rights are different if your property is listed or in a conservation area. Permitted development rights can be removed in certain areas by Article 4 Directions. If your property is in one of these areas, you may have to submit a planning application for your project even if it's normally permitted development. Check to see if there is an Article 4 direction in your area, or if your property is listed or in a conservation area.
For peace of mind, if you do not need planning permission you may still choose to apply for a lawful development certificate (LDC). This is not the same as planning permission but is proof that your household building work is lawful.
You don’t need to own all of the land involved in the application, but you do need to tell all the owners that you’re seeking permission on their land. If you lease a flat, this could be a freeholder or other leaseholders.
Other consents you may need
Listed building consent will nearly always be required for works to a listed building. This includes works to the interior of a listed building and to structures within its curtilage. It is a criminal offence to undertake works that require listed building consent without the necessary consents in place.
You can apply for listed building consent using the same steps as applying for planning permission.