Green belt (paraphrase from NPPF) is a special designation of land which is preserved for its own sake. Land is designated ‘Green Belt’ by local authorities to resist urbanisation. As such it can be incredibly difficult to obtain planning permission to build on these areas.
Green Belt covers an estimated 12.5% of the country (over 1.6 million hectares). Some Local Planning Authorities like Epping Forest, Warrington, and Cheshire have as high as 99.4% of their area designated as Green Belt. These areas have a high degree of land set to pasture, parks, forests and open countryside.