Abandoned plans to switch the fighter aircraft for the Royal Navy's new carriers will cost taxpayers £74 million, according to a public spending watchdog.
Under proposals set out in the 2010 strategic defence and security review (SDSR), the coalition had intended to switch to the more capable F-35C carrier variant of the aircraft - even though it meant mothballing one of the two carriers on grounds of affordability - but the costs of fitting the necessary catapults and arrester gear, ''cats and traps'', had more than doubled to £2 billion.
Although the department "acted quickly" once it had realised the problems with switching, the decision made in the defence review was based on "immature data and flawed assumptions", and the subsequent work cost about £74 million, the National Audit Office (NAO) said.
Margaret Hodge, who chairs the Public Accounts Committee, said the u-turn was the result of "wildly over-optimistic assumptions" made in the SDSR and called for the MoD to "get a grip on this ongoing fiasco".
She said: "The saga of the terrible waste of public money on the Carrier Strike project continues. This report shows that a further £74 million at least has been thrown away on top of the billions of pounds of notes already torn up. When this programme got the green light in 2007, we were supposed to get two aircraft carriers, available from 2016 and 2018, at a cost to the taxpayer of £3.65 billion. We are now on course to spend £5.5 billion, get one operational carrier and have no aircraft carrier capability for nearly a decade."
Ms Hodge added: "This latest u-turn came about because the decisions taken in the SDSR were based on the same wildly over-optimistic assumptions and poor understanding of costs and risks that have characterised this programme from the start. We are also now looking at a further delay of another two years because the ministry has decided to postpone the early-warning system that is a key part of the carrier programme.
"This means the UK will have no carrier Strike operating capability until 2022. What the Ministry of Defence needs to do now is stop backtracking on decisions and haemorrhaging money, and finally get a grip on this ongoing fiasco."
The 2012 decision to switch back to jump jets will be £1.2 billion cheaper than the carrier variant over the next decade, according to the MoD.
Amyas Morse, head of the NAO, said: "It is good that the MoD acted promptly, once it became clear that pursuing the option to buy the carrier variant aircraft would cost a lot more money and add another three years to the whole programme. But to achieve value for money in this project, the department will have to manage significant technical and affordability risks, and be consistent in sticking to the present plan."