The Town and Country Planning (General Permitted Development) (England) Order 2015 No. 596

SCHEDULE 2 Permitted development rights

PART 19 Development by the Crown or for national security purposes

Class B – extension or alteration of an operational Crown building

Development not permitted

B.1  Development is not permitted by Class B if—

(a) the building as extended or altered is to be used for purposes other than those of—

(i) the Crown; or

(ii) the provision of employee facilities;

(b) the height of the building as extended or altered would exceed the height of the original building;

(c) the cubic content of the original building would be exceeded by more than—

(i) 10%, in respect of development on any article 2(3) land; or

(ii) 25%, in any other case;

(d) the floor space of the original building would be exceeded by more than—

(i) 500 square metres in respect of development on any article 2(3) land; or

(ii) 1,000 square metres in any other case;

(e) the external appearance of the original building would be materially affected;

(f) any part of the building as extended or altered would be within 5 metres of any boundary of the curtilage of the original building; or

(g) the development would lead to a reduction in the space available for the parking or turning of vehicles.