protective works, whether temporary or permanent, before or during the construction of the  specified works (including the provision of flood banks, walls or embankments or other new  works and the strengthening, repair or renewal of existing banks, walls or embankments) as are  reasonably necessary—  by reason of any specified work.  (6) Any specified work, and all protective works required by the Agency under sub-paragraph  (4) must be constructed—  and the Agency is entitled by its officers to watch and inspect the construction of such works.  (7) If the Agency reasonably requires, the undertaker must construct all or part of the protective  works so that they are in place prior to the construction of any specified work.  20.  The undertaker must give to the Agency notice in writing of the commencement of any  specified work not less than 14 days prior to its commencement and notice in writing of its  completion not later than 7 days after such completion.  21. —(1) If any part of a specified work or any protective work required by the Agency is  constructed otherwise than in accordance with the requirements of this Part of this Schedule, the  Agency may by notice in writing require the undertaker, at the undertaker’s own expense, to  comply with the requirements of this Part of this Schedule or (if the undertaker so elects and the  Agency in writing consents, such consent not to be unreasonably withheld or delayed) to remove,  alter or pull down the work to the reasonable satisfaction of the Agency, and where removal is  required, to restore the site to its former condition to such extent and within such limits as the  Agency reasonably requires.  (2) Subject to sub-paragraph (3) if within a reasonable period, being not less than 28 days  beginning with the date when a notice under sub-paragraph (1) is served upon the undertaker, the  undertaker has failed to begin taking steps to comply with the requirements of the notice and has  not subsequently made reasonably expeditious progress towards their implementation, the Agency  may execute the works specified in the notice and any expenditure incurred by the Agency in so  doing is recoverable from the undertaker.  (3) In the event of any dispute as to whether sub-paragraph (2) is properly applicable to any  work in respect of which a notice has been served under that sub-paragraph, or as to the  reasonableness of any requirement of such a notice, the Agency must not, except in an emergency,  exercise the powers conferred by sub-paragraph (2) until the dispute has been finally determined  in accordance with paragraph 30.  22. —(1) Subject to sub-paragraph (6) the undertaker must from the commencement of the  construction of the specified works maintain in good repair and condition and free from  obstruction any drainage work which is situated within the limits of deviation and on land held by  the undertaker for the purposes of or in connection with the specified works, whether or not the  drainage work is constructed under the powers conferred by this Order or is already in existence.  (2) If any such drainage work which the undertaker is liable to maintain is not maintained to the  reasonable satisfaction of the Agency, the Agency may by notice in writing require the undertaker  to repair and restore the work, or any part of such work, or (if the undertaker so elects and the  Agency in writing consents, such consent not to be unreasonably withheld or delayed), to remove  the work and restore the site to its former condition, to such extent and within such limits as the  Agency reasonably requires.  (3) Subject to sub-paragraph (5) and paragraph 26, if, within a reasonable period, being not less  than 28 days beginning with the date on which a notice in respect of any drainage work is served  131 (a) to safeguard any drainage work against damage; or  (b) to secure that its efficiency for flood defence purposes is not impaired and that the risk of  flooding is not otherwise increased,  (a) without unreasonable delay in accordance with the plan approved under this Schedule;  and  (b) to the reasonable satisfaction of the Agency, 