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

B.2    Development not permitted

Development is not permitted by Class B(a) if—

(a)the height of any building would be increased;

(b)the cubic content of the original building would be increased by more than 10%;

(c)any part of any new building would be more than 30 metres from the original building;

(d)the development would involve the extension, alteration or provision of a dwelling;

(e)any part of the development would be carried out within 5 metres of any boundary of the unit; or

(f)the ground area of any building extended by virtue of Class B(a) would exceed 465 square metres.