The Town and Country Planning (General Permitted Development) Order 1995

A.1    Development not permitted

Development is not permitted by Class A if—

(a) the plant or machinery would—

(i) if the land or pier is within 3 kilometres of the perimeter of an aerodrome, exceed a height of 25 metres or the height of the highest existing structure (whichever is the lesser), or

(ii) in any other case, exceed a height of 25 metres;

(b) in the case of an extension to an existing building or structure, that building or structure would as a result exceed 5 metres above ground level or the height of the roof of the existing building or structure, whichever is the greater, or

(c) in any other case, the height of the building or structure erected, extended, altered or replaced would exceed 5 metres above ground level.