Where, by virtue of any of the previous provisions of this Chapter, any survey is required to be carried out, or any local plan or proposals for the alteration, . . .or replacement of such a plan or of a structure plan are required to be prepared or submitted to the Secretary of State, or steps are required to be taken for the adoption of any local plan or any such proposals, then—
the Secretary of State may carry out the survey or prepare and make a local plan or, as the case may be, alter, . . . or replace such a plan or a structure plan, as he thinks fit.
Where under subsection (1) the Secretary of State may do anything which should have been done by a local planning authority ("the defaulting authority") he may, if he thinks fit, authorise any other local planning authority who appear to him to have an interest in the proper planning of the area of the defaulting authority to do it.
The previous provisions of this Chapter shall, so far as applicable, apply with any necessary modifications in relation to the doing of anything under this section by the Secretary of State or an authority other than the defaulting authority and the thing so done.
The defaulting authority—