Tube infrastructure consortium Metronet said that Keith Clarke, the chief executive of Atkins, would be replaced as its chairman 鈥渁t some point in the future鈥�.

A spokesperson for the consortium, which includes Balfour Beatty, said 鈥渋t was never meant to be a long-term appointment鈥�, but that Clarke would not be leaving imminently.

She said his departure was not linked to a report released last Thursday by Chris Bolt, the PPP arbiter, which stated that after three years鈥� work on the underground Metronet was significantly behind schedule in its work on stations.

Metronet has called on the arbiter to decide which party is responsible for 拢750m in cost overruns, if its performance does not improve by 2010. Metronet will be informed of the decision before the end of January.

The spokesperson said: 鈥淚t鈥檚 important to realise that the 拢750m is not an overspend. It is an adverse cost, some of which has already been spent, such as 拢80-90m on the Central Line fleet, but some is to be spent in the next seven-and-a-half-years, up to 2010.鈥�