A local planning authority may at any time prepare proposals—
for alterations to the local plan for their area; or
for its replacement.
A local planning authority shall—
consider whether they need to prepare such proposals, if they have been supplied with a statement under section 35C that the local plan is not in general conformity with the structure plan; and
prepare such proposals, if they are directed to do so by the Secretary of State, within such period (if any) as he may direct.
An authority shall not, without the consent of the Secretary of State, prepare such proposals if the plan or any part of it has been approved by the Secretary of State.
Proposals for the alteration of a local plan may relate to the whole or part of the area to which the plan relates.
Subject to the following provisions of this Chapter and section 287, proposals for the alteration or replacement of a local plan shall become operative on the date on which they are adopted.