A report by the House of Commons Public Accounts Committee report claims the part-privatisation of the Tube has cost taxpayers almost £1bn.
The report also says that maintaining and upgrading the tube will cost £450m more under the scheme than if the work was finance by the government.
A TfL spokesman said: "TfL has consistently said that the London Underground PPP deals are an expensive and over complicated way to manage the maintenance and renewal of the Tube.
