11. If—
(a)any alterations or additions, either permanent or temporary, to railway property are reasonably required during the construction of any relevant work, or during a period of 12 months commencing with the date of completion of that work, in consequence of the construction of that relevant work; and
(b)Network Rail gives to the undertaker reasonable notice of its intention to carry out those alterations or additions, specifying the alterations or additions in question,
the undertaker must pay to Network Rail the reasonable cost of carrying out those alterations or additions.