11.—(1) No part of the authorised development is to commence until for that part written details of the surface and foul water drainage system, reflecting the mitigation measures in chapter 14 of the environmental statement and including means of pollution control, have been submitted to and approved in writing by the Secretary of State following consultation with the relevant local authority and the Environment Agency on matters relating to their functions.
(2) The surface and foul water drainage system must be constructed in accordance with the approved details referred to in paragraph (1) unless otherwise agreed in writing by the Secretary of State following consultation with the relevant local authority and the Environment Agency on matters relating to their functions, provided that the Secretary of State is satisfied that any amendments to the approved details would not give rise to any materially new or materially different environmental effects in comparison with those reported in the environmental statement.