Question Author
After a lot of "googling" I've found this from the Coast Protection Legislation of 1949.....
18 Prohibition of excavation etc., of materials on or under the seashore.
(1)Subject to the provisions of this section, and notwithstanding anything contained in any other enactment, it shall be unlawful to excavate or remove any materials (other than minerals more than fifty feet below the surface) on, under or forming part of any portion of the seashore to which the provisions of this section are applied.
(2)The provisions of the last foregoing subsection shall not affect the excavation or removal of any materials by the [F44Secretary of State] in the exercise of the powers conferred upon him by Part II of this Act, or the excavation or removal thereof by any other person in compliance with a notice served by that [F44Secretary of State] under the said Part II.
(3)A coast protection authority may make an order applying the provisions of this section to any such portion of the seashore within their area or [F45of the sea–shore lying to seaward of their area but within three nautical miles of the baselines from which the breadth of the territorial sea adjacent to Great Britain is measured,] as may be described in the order:
Provided that the order may, as respects the whole of that portion of the seashore or any such part thereof as may be specified in the order, except from the provisions of subsection (1) of this section the carrying out of operations of any such class as may be so specified, and any such exception may be either unconditional or subject to such conditions as may be specified in the order.