An influential committee of MPs has lambasted the Ministry of Defence (MoD) for "astonishing" failures in procuring the RAF's new £10.5 billion fleet of tanker and transport aircraft.
The Public Accounts Committee (PAC) said the department signed up to the biggest Public Finance Initiative (PFI) contract for the key kit even though it had no idea whether the deal was good value for money.
The taxpayer also faces paying out hundreds of millions of pounds more because the aircraft do not have sufficient protection to fly on operations in Afghanistan.
The criticism came in the PAC's report into the Future Strategic Tanker Aircraft (FSTA) project.
The MPs condemned the fact that it took nine years of negotiation before the complex 27-year contract with AirTanker Ltd was sealed in 2008, and pointed out that no other country used PFI to procure defence equipment.
The refuelling and transport aircraft, which are meant to replace the RAF's ageing Tristar and VC10 fleet, are now due to start coming into service next October - five and a half years behind schedule.
They also questioned why the MoD had rejected advice from its own project team in 2004 that the deal should be abandoned because of "significant concerns" over the company's bid.
Committee chairwoman Margaret Hodge said using PFI for the FSTA had been "inappropriate" and it was "no excuse" that such arrangements were favoured across government at the time.
"PFI may be suited to projects like building schools or hospitals where there is a clear specification," the Labour MP for Barking said. "Defence programmes are by their nature different - activities and demands are far less predictable and much more susceptible to change.
"It is simply astonishing that it took until 2006 for the department to recognise that the new aircraft should be able to fly into high threat environments like Afghanistan. Four years later, it has still not decided whether to fit the necessary protective equipment to the aircraft which is essential if they are to be used in Afghanistan."