Also, your back garden is Brownfield land, so if you have a large back garden and build another house on it, it counts towards Prescotts target of building houses on brownfield land, when in fact you are concreting over a green space.
Historically airfields were green field sites, but where there were buildings it was brownfield, this made it more difficult to get planning to build on an airfield. Now we have new improved
designations, and the whole airfiled is brownfield, and therefore planning is much easier to get - prepare to see many small civil airfields dissappear over the next decade.