Unless a project falls within the scope of Permitted Development (applicable to certain minor types of building work like small conservatories, for instance), all building projects must have planning approval.
Planning permission is the responsibility of the local authority planning department which is concerned with the visual appearance of the proposed work, its height and size and whether it is sympathetic to its location, whether it will overlook neighbouring properties, its distance from the road, and whether it conforms to the local plan.
Miriam Layton will work with you to develop the design and then prepare the architectural drawings and documents needed for submission of the Planning Application, guide you through the process and keep you informed throughout.
Information about the planning process can be found on the Planning Portal
Do you need permission? Find out using the Interactive House