s 21 Alteration or replacement of unitary development plan.
(1) A local planning authority may at any time prepare proposals— (a) for alterations to the unitary development plan for their area; or (b) for its replacement. (1A) If the Secretary of State directs them to do so, the authority shall prepare, within such time as he may direct, proposals for— (a) such alterations to the unitary development plan as he directs; or (b) its replacement. (1B) An authority shall not, without the consent of the Secretary of State, prepare proposals in respect of a unitary development plan if the plan or any part of it has been approved by the Secretary of State. (2) . . .Sections 12 to 20 (other than subsection (1) of section 12) shall apply in relation to the making of proposals under this section and to any alteration or replacement so proposed as they apply to the preparation of a unitary development plan under section 12 and to a plan prepared under that section. (3) As soon as practicable after— (a) an order has been made under paragraph 5 of Schedule 32 to the Local Government, Planning and Land Act 1980 (designation of enterprise zone); or (b) a notification has been given under paragraph 11(1) of that Schedule (approval of modification of enterprise zone scheme), the local planning authority for an area in which the zone is wholly or partly situated shall review any unitary development plan for that area in the light of the provisions of the scheme or modified scheme under that Schedule and prepare proposals under this section for any consequential alterations to the plan which they consider necessary.