A public body’s notice comes into force when it is accepted by the local authorty, either by notice given within the prescribed period to the public body by which it was given or by virtue of section 54(3) of this Act, and, subject to paragraph 3(3) below, continues in force until the occurrance of, or the expiry of a prescribed period of time beginning on the date of such event as may be prescribed.

Building regulations may empower a local authority to extend (whether before or after its expiry) any such period of time as is referred to in sub-paragraph (1) above.