If during the construction of a specified work or during a period of 12 months after the completion of that work any alterations or additions, either permanent or temporary, to railway property are reasonably necessary in consequence of the construction of a specified work in order to ensure the safety of railway property or the continued safe and efficient operation of the railways of Railtrack PLC, and Railtrack PLC gives to the Council reasonable notice of its intention to cary out such alterations or additions (which shall be specified in the notice), the Council shall pay to Railtrack PLC the reasonable cost of those alterations or additions including, in respect of any such alterations or additions as are to be permanent, a capitalised sum representing the increase of the costs which may be expected to be reasonably incurred by Railtrack in maintaining, working and, when necessary, renewing any such alterations or additions.

The engineer shall, in respect of the capitalised sums referred to in this paragraph and paragraph 9(a), provide such details of the formula by which those sums have been calculated as the Council may reasonably require.

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 saving shall be set off against any sum payable by the Council to Railtrack PLC under this paragraph.