(1) A notice given under this Part may be revoked or varied by a subsequent notice or notices.
(2) A notice may be varied by modification of, or addition to, its terms and specifications.
(3) Without limiting the above, a notice may be varied by extending the time for complying with the notice.
(4) A notice may only be revoked or varied by--(a) the Environment Agency Head, or(b) the authorised officer who gave the notice, or(c) another authorised officer.