Ministry of Defence is to revert to Labour's original plan – dismissed by PM as 'more expensive and less capable'

The Ministry of Defence is to abandon plans to buy the preferred fighter for the Royal Navy's new aircraft carriers, in an embarrassing U-turn for David Cameron.

The prime minister personally endorsed the decision to equip the over-budget carriers with "cats and traps" so they could catapult and recover a version of the F-35 joint strike fighter (JSF) from their decks.

But the cost of converting the carriers has already reached £2bn, and the JSF model Downing Street wanted has been beset by delays and technical problems.

The aircraft will now not be ready until 2023 at the earliest, forcing the government to revert to Labour's original plans to buy the less capable jump jet model.

Philip Hammond, the defence secretary, is due to make an announcement in the Commons on Thursday explaining the about-face, which was approved by the National Security Council on Tuesday.

He had hoped to persuade Downing Street to make the move at the end of March, so the MoD could finalise its budget before the new financial year. But Cameron is understood to have blocked the move, insisting the Treasury undertake a new analysis of the costs, while the MoD was told to check its own calculations again.

The prime Mminister has now had to concede to Hammond, and will face taunts from Labour, which denounced the JSF "upgrade" when it was announced with some fanfare in the 2010 strategic defence and security review (SDSR).

"The decision to revert was clear cut," said a senior defence source. "The government could not accept the delays. Once the facts had changed, it would have been wrong to plough on. Ministers always said they wouldn't be afraid to change course."

The government will argue there are benefits to U-turning now. Without the complex conversion to cats and traps, the first new carrier could be ready for service by 2018, two years ahead of schedule.

Though the navy will not have the JSF it wanted, the alternative model is already in production and the MoD can expect the first delivery of aircraft in 2016.

But the announcement is a rebuff to Cameron and his deputy, Nick Clegg.

The decision over which fighters would be used on the two new Queen Elizabeth-class aircraft carriers was one of the most significant announcements in the SDSR and came as the government approved redundancy rounds and budget cuts for all three services. The aircraft carrier Ark Royal was scrapped, along with the Harrier jump jet fleet, to save money that was needed to fund the new carrier programme.

Cameron pushed the military to ditch the F-35B version of the JSF, an aircraft that can take off and land in a similar way to a Harrier. Instead, he and Clegg chose the F-35C, which has a longer range and can carry more weapons.

Explaining the decision to MPs, Cameron said Labour had got it "badly wrong", and insisted changing the carriers to cats and traps would make it easier for the navy to work with France and the US.

One defence source distanced the MoD from this argument, saying it was "meaningless window dressing", but admitted the costs and delays of the carrier variant of the JSF – and the money that would need to be spent on converting the carriers – had forced Hammond's hand. The navy will hope that the second aircraft carrier, which was due to be mothballed as soon as it was completed, will now be reprieved and made ready for service.

Jim Murphy, the shadow defence secretary, has repeatedly criticised the SDSR, and said the confusion over which JSF would end up on the carriers was a "mess entirely of ministers' own making.

"The government's chaotic carrier policy totally undermines their credibility on defence. This is a personal humiliation for David Cameron, who will have to return to Labour's policy, which he previously condemned. This is a strategically vital element of the equipment programme on which our security and thousands of jobs depend and yet ministers have treated it with hubristic incompetence.

"Scrapping the Harriers to leave Britain without aircraft to fly from aircraft carriers for at least a decade appears increasingly inexplicable. We need a plan to restore Britain's power and prestige at sea, which was so damaged by the discredited defence review, and there are crucial questions on cost and capability ministers must answer."

The government maintains Labour's criticisms are opportunistic, pointing to a £38bn defence budget "black hole" left by the previous government.

What David Cameron said about the JSF

In the foreword of the 2010 Strategic Defence and Security Review:

"The last government committed to carriers that would have been unable to work properly with our closest military allies. It will take time to rectify this error, but we are determined to do so. We will fit a catapult to the operational carrier to enable it to fly a version of the joint strike fighter with a longer range and able to carry more weapons. Crucially, that will allow our carrier to operate in tandem with the US and French navies, and for American and French aircraft to operate from our carrier and vice-versa."

The SDSR, which was signed off by Cameron and Nick Clegg, the deputy prime minister, said the F-35C would be "more cost effective … it has greater range, payload and versatility than the [F-35B].

Speaking in the House of Commons in October 2010:

"This is another area where I believe the last government got it badly wrong … The carriers they ordered were unable to work effectively with our key defence partners, the United States or France … They ordered the more expensive and less capable version of the joint strike fighter to fly off the carriers … That is the legacy we inherited, an appalling legacy the British people have every right to be angry about, but I say to them today: we will act in the national interest …

"It will take time to rectify these mistakes, but this is how we intend to do so. We will build both carriers, but hold one in extended readiness. We will fit the "cats and traps" – the catapults and arrester gear – to the operational carrier. This will allow our allies to operate from our operational carrier, and it will allow us to buy the carrier version of the joint strike fighter, which is more capable, less expensive, has a longer range and carries more weapons. We will also aim to bring the planes and the carriers in at the same time."