Longman Dictionary of Contemporary English
Wiktionary
n. (context British English) legal permission to construct on one's land, or to change the use of the land.
Wikipedia
Planning permission or planning consent is the permission required in the United Kingdom and Ireland in order to be allowed to build on land, or change the use of land or buildings. Within the UK the occupier of any land or building will need title to that land or building (i.e. "ownership"), but will also need "planning title" or planning permission. Planning title was granted for all pre-existing uses and buildings by the Town and Country Planning Act 1947, which came into effect on 1 July 1948. Since that date any new "development" has required planning permission. "Development" as defined by law consists of any building, engineering or mining operation, or the making of a material change of use in any land or building. Certain types of operation such as routine maintenance of an existing building are specifically excluded from the definition of development. Specified categories of minor or insignificant development are granted an automatic planning permission by law, and therefore do not require any application for planning permission. These categories are referred to as permitted development.
In the case of any proposal there is therefore a two-stage test: "is the proposal development at all?" and, if the proposal is development, "is it permitted development?" Only if a development is not permitted development would an application for planning permission be required. An application for planning permission should be made to the local planning authority (LPA).
LPAs are generally the local borough or district council ( 'local authority' in Scotland), although an application for a mining operation, minerals extraction, or a waste management facility would be decided by the local county council in non-metropolitan areas. Within a national park planning applications are submitted to the national park authority.
All LPAs have their own website which will access relevant application forms, contact details and other relevant documents. They are generally receptive to pre-application discussion in order to clarify whether a proposal will require planning permission and, assuming that it does, the probability of such planning permission being granted.