The Metropolitan Green Belt is a statutory green belt around London, England. It includes designated parts of Greater London and the surrounding counties of Bedfordshire, Berkshire, Buckinghamshire, Essex, Hertfordshire, Kent and Surrey in the South East and East of England regions.
The term emerged from continental Europe where buffer zones and broad boulevards were increasingly used to separate new development from the centre of historic towns; most notably the Ringstraße in Vienna. Various proposals were put forward from 1890 onwards but the first to garner widespread support was put forward by the London Society in its "Development Plan of Greater London" 1919. Alongside the CPRE they lobbied for a continuous belt (of up to two miles wide) to prevent urban sprawl, beyond which new development could occur.
Implementation of the notion dated from Herbert Morrison's 1934 leadership of the London County Council. It was first formally proposed by the Greater London Regional Planning Committee in 1935, "to provide a reserve supply of public open spaces and of recreational areas and to establish a green belt or girdle of open space". It was again included in an advisory Greater London Plan prepared by Patrick Abercrombie in 1944 (which sought a belt of up to six miles wide). However, it was some 14 years before the elected local authorities responsible for the area around London had all defined the area on scaled maps with some precision (encouraged by Duncan Sandys to designate a belt of some 7–10 miles wide).