9.—(1) If any permanent or temporary alterations or additions to railway property are reasonably necessary in consequence of the construction of a specified work or during a period of 24 months after the completion of that work in order to ensure the safety of railway property or the continued safe and efficient operation of the railway of Network Rail, such alterations and additions may be carried out by Network Rail.
(2) If Network Rail gives to the undertaker reasonable notice of its intention to carry out such alterations or additions (which must be specified in the notice), the undertaker must pay to Network Rail the reasonable cost of those alterations or additions including, in respect of any such alterations and additions as are to be permanent, a capitalised sum representing the increase of the costs that may be expected to be reasonably incurred by Network Rail in maintaining, working and, when necessary, renewing any such alterations or additions.
(3) If during the construction of a specified work by the undertaker, Network Rail gives notice to the undertaker that Network Rail itself desires to construct that part of the specified work that in the opinion of the engineer is endangering the stability of railway property or the safe operation of traffic on the railways of Network Rail then, if the undertaker decides that part of the specified work is to be constructed, Network Rail must assume construction of that part of the specified work and the undertaker must, despite any approval of the specified work under paragraph 5(1), pay to Network Rail all reasonable expenses to which Network Rail may be put and compensation for any loss which it may suffer by means of the execution by Network Rail of that specified work.
(4) The engineer must, in respect of the capitalised sums referred to in this paragraph and paragraph 10(a), provide such details of the formula by which those sums have been calculated as the undertaker may reasonably require.
(5) If the cost of maintaining, working or renewing railway property is reduced in consequence of any such alterations or additions, a capitalised sum representing such savings must be set off against any such sum payable by the undertaker to Network Rail under this paragraph.