David Cameron has signed off a U-turn on controversial plans for Britain's aircraft carriers.
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The prime minister has given Defence Secretary Phillip Hammond the green light to revert to the previous Labour administration's plans to buy the conventional jump-jet version of the F35 Joint Strike Fighter.
Their decision marks an about-turn in what had been a central plank of the coalition government's defence strategy. The government had announced in the defence review of 2010, that it would buy the F35 Joint Striker Fighter carrier version, rather than the jump-jet version.
The decision was keenly backed by Mr Cameron as it would have allowed Britain to operate more closely with France and the United States.
It is understood that Mr Hammond will announce the changes at the House of Commons tomorrow, saying that the decision will save hundreds of millions of pounds.
Catapult and traps
The defence secretary's decision follows a meeting with the National Security Council, in which members discussed how the F35 carrier version would have been too expensive as it required the installation of a "catapult and traps" launch system to the new Queen Elizabeth-class aircraft system.
Costs for converting the carrier to the new aircraft type have reportedly risen from £1.2 bn to £2bn. Original Ministry of Defence estimates had been said to have suggested the cost of the work would have been around £400m.
However Labour seized on the reversal, saying that returning to their original plans would cost taxpayers £250m.
Shadow defence secretary Jim Murphy told Channel 4 News: "If this is confirmed, it's a real shambles. The government's spent £250m of taxpayers' money on a decision on an aircraft carrier and an aeroplane, and are now about to do a U-turn back to Labour's old policy, and in the meantime, sell all the harrier jump jets to the Americans at a knock-down price, and we're not going to have airplanes or aircraft carriers for a decade.
"This is a personal humiliation for the prime minister. This was a big decision for David Cameron. The U-turn, when it comes, will reduce our capability and will cost us more money."
Reverting to the F35-B vertical landing model is now believed to bring the launch date closer, to 2018, with sea trials expected to begin in 2017.
The government had previously said that installing catapults on the carriers would delay the arrival of the new vessels until at least 2020, with some sources suggesting they would not be ready before 2023.
Mr Hammond said that any decision would be fully explained. He said: "The Labour Party don't know what the decision is that we're going to announce shortly and putting any kind of figure on it will be sheer guess work on their part.
"We will make an announcement to Parliament and we will be completely transparent about the prcess we have gone through - how we've arrived at the decision that we have, and what the level of any costs involved are."
Defence analysts said that while a decision to revert to the F35 jump-jet would be cheaper in the short term, it could prove costly in the long run.
Edward Hunt, senior consultant of IHS Jane's, said of the F35 jump-jet: "The vertical take off one is more complicated. It requires a big old lift van behind the engine which cuts fuel room and cuts internal weapons carriage room.
"The carrier version has larger wings, more space inside for weapons and fuel, so it gives it a longer range.
"Not only can it carry weapons, it can bring them back if it doesn't drop them. One of the problems with the B [jump-jet version] is that you might have to end up dropping very expensive weapons into the sea if you can't land with them."
He added: "The cost estimates for fitting the catapults and the carriers for using the C [carrier] variant are such that the decision's basically been taken on what appears to be saving money in the short term.
"That may prove to be a problem over the 40, 50, 60 years that the carrier vessels are in service."