As time goes on .... the cross bar that needs to be jumped by any interested party rises

Alan Bloom Ernst & Young

But if Railtrack's successor is a non-profit company without shareholders, the government's preference, taxpayers could end up footing the bill.

Ministers have already given Railtrack �2.9bn to pay for Transport Secretary Stephen Byers's decision to call in administrators in October.

But that will run out at the end of March and experts at Ernst and Young predict they will be running the company until September.

No gift

That will mean an estimated extra �1.9bn is needed, administrator Chris Hill told the Transport Select Committee.

A spokesman for the Department of Transport says money which the government puts into Railtrack to keep it going while it is in administration "is not a gift".

Railtrack also plans to ask for more cash to cope with the aftermath of the Hatfield rail disaster.

Conservative MP Christopher Grayling warned that this �4.8bn bill might jeopardise plans to take the firm out of administration because it was bigger than its valuation.

Afterwards the Epsom and Ewell MP described the figures given to MPs by Railtrack and its administrators as "completely astounding".

He said that whoever wanted to buy Railtrack would have to pay out �5bn.

"If it goes to the company limited by guarantee it will have to come from taxpayers," he said.

Alan Bloom, Mr Hill's colleague at Ernst & Young, said: "As time goes on .... the cross bar that needs to be jumped by any interested party rises."

"We are confident that there will be bidders out there that will be prepared at the very least to come up with a proposal that gives value for the creditors."