Pilots of the RAF's most advanced fighter jets are being grounded because shortages of aircraft spares mean they cannot put in enough flying hours to keep their skills up to date, MPs have warned.
The Commons Public Accounts Committee said five Typhoon pilots had to be temporarily grounded last year because a lack of aircraft availability meant they could not do the required flying time.
It said the shortages were also affecting the training programme, with only eight of RAF's 48 Typhoon pilots qualified for ground attack operations - the role it is being used for in Libya.
The RAF is currently having to cannibalise aircraft for spare parts in order to keep the maximum number of Typhoons in the air on any given day. The committee said the Ministry of Defence had warned the problems were likely to continue until 2015 when it expects the supply of spares finally to have reached a "steady state".
Overall, it said that while the MoD was now buying 30% fewer Typhoons than it had originally planned, the cost of the project had risen by an estimated £3.5 billion - representing a 75% increase in the cost of each individual aircraft.
When the MoD first entered into the contract for the Eurofighter, as it was then known, in 1998 in collaboration with Germany, Italy and Spain, it had envisaged buying a total of 232 aircraft in three tranches. That has since been cut to 160 - with the 53 oldest aircraft due to be retired from service by 2019, leaving a long-term fleet of 107 aircraft.
The overall cost of the programme is now estimated at £20.2 billion - £3.5 billion more than the original budget - with the cost per plane rising from £72 million to £126 million. The committee complained that the MoD had been unable to offer a "coherent explanation" for a decision in 2004 to equip the early Typhoons for ground attack operations at a cost of £119 million, only to switch them back to an air defence role in 2009, a year after the upgrade was finally ready.
However, Defence Secretary Liam Fox said the project was "under control and back on track".
"The NAO's March report concluded that after years of financial mismanagement and project delays under the previous government, the Typhoon project has been turned around," he said. "The project is finally under control and back on track. The PAC report recognises that the MoD and industry have worked to resolve spares issues and performance targets are now being met."
He added: "I am determined that in the future such projects are properly run from the outset, and I have announced reforms to reduce equipment delays and cost overruns. I will also chair regular major projects review boards to ensure our armed forces are well equipped and taxpayers get value for money."