If you propose to erect or alter a building, change the use of a building or land, form a vehicle access, or carry out work that can be described as an engineering operation, you may require planning permission
However certain developments do not require permission as they constitute ‘permitted development’ as laid out in the Town and Country Planning (General Permitted Development) Order. Whilst such developments do not require planning permission, if you have any doubts, or if you would like a formal confirmation that a development does not require planning permission and is lawful, you should submit an application for a Certificate of Lawful Development.
Permitted Development rights do not exist if:
1) The property is a flat, maisonette or used for any business.
2) Your house has had its 'permitted development' rights removed. (These are rights that allow you to do work without needing to ask permission. They are most often removed by a condition which was set when the original permission to build your house was granted. This is more likely if that was within the past 30 years - please check with the Development Management team.)
You can apply for a Certificate of Lawful development which will formally confirm whether planning is required at the Planning Portal
You can discuss your proposed scheme with a member of Development Management. However any advice given would only be informal and no confirmation from Development Management can be provided in writing except through the submission of a Certificate of Lawful Development, or if relevant, a Prior Approval application in the case of deeper single-storey rear extensions.
You can also use the following tools on the Planning Portal to see if you need planning permission and to help you with your application.
Interactive house guide
Interactive terrace/flat/shop/basement guide