Normally building work and changes of use require planning permission. However, in some cases this permission is granted automatically by national legislation (and is referred to as “permitted development”) so you will not need to make a planning application for it.
The most commonly encountered categories of permitted development are those relating to alterations and extension to houses and bungalows and for outbuildings and other structures within their grounds. If you live in a flat (either in a block with other flats or above a shop or offices), you will not have permitted development rights so you will have to make planning applications for such works.
Although permitted development is effectively a nationwide planning permission, in some instances these rights will have been taken away by planning conditions imposed on a development, e.g. when a new housing estate is built. Local authorities can also introduce what are called "Article 4 Directions" which take away these rights. These are most frequently used in conservation areas. They restrict the scope of permitted development rights either in relation to a particular area or site, or a particular type of development anywhere in the authority’s area. If you are assessing whether a proposal is permitted development, you need to be aware that one of these local controls might affect the rights.
Regardless of whether you need planning permission, you will normally need approval under the Building Regulations. These are separate to planning permission and we do not address them in this guidance. There may also be restrictions imposed by previous owners of your property known as “restrictive covenants”. These might either require you to obtain permission for alterations, etc or may prevent you carrying out certain types of development.