40.—(1) Subject to subsection (2), a permission granted under F439[this Part or Part XXI], shall on the expiration of the appropriate period (but without prejudice to the validity of anything done pursuant thereto prior to the expiration of that period) cease to have effect as regards—

(a) in case the development to which the permission relates is not commenced during that period, the entire development, and

(b) in case the development is commenced during that period, so much of the development as is not completed within that period.

(2) (a) Subsection (1) shall not apply—

(i) to any permission for the retention on land of any structure,

(ii) to any permission granted either for a limited period only or subject to a condition which is of a kind described in section 34(4)(n),

(iii) in the case of a house, shop, office or other building which itself has been completed, in relation to the provision of any structure or works included in the relevant permission and which are either necessary for or ancillary or incidental to the use of the building in accordance with that permission, or

(iv) in the case of a development comprising a number of buildings of which only some have been completed, in relation to the provision of roads, services and open spaces included in the relevant permission and which are necessary for or ancillary or incidental to the completed buildings.

(b) Subsection (1) shall not affect—

(i) the continuance of any use, in accordance with a permission, of land,

(ii) where a development has been completed (whether to an extent described in paragraph (a) or otherwise), the obligation of any person to comply with any condition attached to the relevant permission whereby something is required either to be done or not to be done.

(3) F438[In this section and sections 42 and 42A,], “the appropriate period” means—

(a) in case in relation to the permission a period is specified pursuant to section 41, that period, and

(b) in any other case, the period of five years beginning on the date of the grant of permission.