Labour MP Alan Williams, a member of the Commons Public Accounts Committee, has asked government departments to submit details of PFI schemes. He wants to know which have been refinanced and which have clawback provisions that permit departments to share in any profit made through taking out cheaper loans.
The National Audit Office found that Carillion and Group 4 made £13m extra profit when they refinanced the debt on the Fazakerley Prison scheme in Liverpool.
Williams said: "Following Fazakerley, there is a real need to ensure that the public interest is properly represented in all this.
"The opportunity for firms to make large windfalls is still there in schemes that were signed prior to the last couple of years when interest rates were still quite high."
Williams has compiled a list of PFI hospitals that do not have a clawback provision. These include the £150m Norwich and Norfolk, signed in January 1998 and built by Laing, and the £94m Dartford and Gravesham, signed in 1997 and built by Carillion.
Williams said most hospital schemes signed before 1999 did not have clawback provisions. He said that that raised the spectre of other contractors making excess profit at a time when the public was complaining that the NHS was starved of money.
He said: "We really do not want companies getting bonanza-level profits through firms taking advantage of lower interest rates. It is fine if they make money through efficiency savings but not through refinancing."
A government insider said: "If Williams' campaign unearths firms that make a killing on hospital schemes, MPs will go bonkers.
"Massive profits for contractors on hospitals that the public feel are underfunded will not make great headlines for the government."
Williams, who raised the issue in parliament this month, conceded that nothing could be done to clawback money from contracts that had reached financial close.
Carillion executive director John Sharples last week insisted that no clawback arrangement had been in place at Fazakerley: "There may still be several schemes that could enjoy a significant upturn through refinancing, but from here on in, the scope is quite limited," he said.