4.—(1) If Network Rail reasonably considers that any relevant work or any part of a relevant work will or may affect the stability of railway property or the safe operation of traffic on its railways, it may elect to construct that relevant work or that part itself by giving notice to the undertaker specifying the work or part in question (“the specified work”) (“y gweithfeydd a bennwyd”) and stating that it desires to construct that work or part.
(2) Notice of an election under sub-paragraph (1) cannot be given after the end of the period of 56 days beginning with the date on which plans of the specified work have been supplied to Network Rail under paragraph 3.
(3) Following an election by Network Rail under sub-paragraph (1), the specified work must not be constructed except by Network Rail in accordance with sub-paragraph (4).
(4) If the undertaker confirms that it desires the specified work to be constructed, Network Rail must construct it (together with any adjoining part of any relevant work which the undertaker reasonably requires to be constructed in one operation with the specified work) on the undertaker’s behalf—
(a)with all reasonable dispatch;
(b)to the reasonable satisfaction of the undertaker;
(c)in accordance with the plans approved or settled under paragraph 3; and
(d)under the supervision (where appropriate and if given) of the undertaker.