22.—(1) With respect to any requirement which requires the authorised development to be carried out in accordance with the details approved by the relevant planning authority or another discharging authority, the approved details must be carried out as approved unless an application for an amendment or variation is previously agreed, by the relevant planning authority or that other discharging authority as specified in the relevant requirement, in accordance with sub-paragraph (2) and in consultation with any body specified in the relevant requirement.
(2) No amendments to or variations from the approved details may be approved if their likely significant effects on the environment are not assessed in the environmental statement, or have not been subject to such further assessment as the relevant planning authority or that other discharging authority may require; provided that such approval must not be given except where it has been demonstrated that the subject-matter of the approval sought is unlikely to give rise to any materially new or materially different environmental effects in comparison with the authorised development as approved (as identified in the environmental statement).
(3) The approved details must be taken to include any amendments that may subsequently be approved by the relevant planning authority or that other discharging authority.
(4) Subject to sub-paragraph (2), if a relevant planning authority which receives an application for approval of any amendments to approved details under sub-paragraph (1) fails to notify the undertaker of its decision before the end of the period of 56 days beginning with the date on which the application was made, such longer period as may be agreed in writing by the undertaker and the relevant authority, it is deemed to have granted consent.