Nothing in any of the provisions of this Part relating to any relevant works power shall authorise any relevant undertaker to carry out any works at any place below the place to which the tide flows at mean high water springs, except in accordance with such plans and sections, and subject to such restrictions, as may, before the works are commenced, have been approved by the Secretary of State.
An approval for the purposes of subsection (1) above shall be given to a relevant undertaker by the service on that undertaker of a notice containing the approval.
In subsection (1) above the reference to a relevant works power is a reference to a power conferred by any of the relevant sewerage provisions or by any of sections 158, 159, 161, 163 and 165 above, except the power conferred by section 161(3).