The Royal Navy has agreed to sacrifice one of its two new aircraft carriers to save about £8.2 billion from the defence budget.

The admirals, who have battled for a decade to secure the two new 65,000-ton carriers, have been forced to back down because of the soaring cost of the American-produced Joint Strike Fighter (JSF) aircraft due to fly off them.

The move is a blow to the navy’s prestige and has come on the heels of Gordon Brown’s announcement last month that he was axing one of the navy’s four Trident nuclear deterrent submarines.

It is too late for the navy to renege on contracts to build the two carriers, the Queen Elizabeth, due to go into service in 2016, and the Prince of Wales, due to follow in 2018. Although the second carrier will be built, it will be used as an amphibious commando ship, with only helicopters on board instead of JSF aircraft.

The move will leave the navy without a carrier when the Queen Elizabeth goes into refit, leaving open the possibility that it might have to borrow one from the French navy. In a meeting with Brown last year, Nicolas Sarkozy, the French president, had suggested that refits of French and British aircraft carriers should be co-ordinated.

The decision to have only one new aircraft carrier will cut the number of JSFs to be flown by RAF squadrons from 138 to about 50, saving £7.6 billion. At current prices, the aircraft will cost close to £90m each, but this could rise to more than £100m.

Using the Prince of Wales as a commando ship will save a further £600m, the amount that would have been needed to replace the amphibious landing ship Ocean, which is due to go out of service in 2018.

The decision to cut the number of JSF aircraft has been agreed by senior navy and air force commanders in discussions preparing for the strategic defence review.

Both Labour and the Conservatives are committed to conducting a strategic defence review after the general election, which must be held by the late spring.

A senior Royal Navy officer said: “We always knew that the real cost of the carrier project is the JSF fleet to go on them. It would cost us at least £12 billion if we bought all the aircraft we originally asked for. We are waking up to the fact that all those planes are unaffordable. More than half of the £5 billion contracts to build the two new carriers have been contracted, so it is too late to get out of building the ships. This way at least we are covered when Ocean goes out of service.”

Since both aircraft carriers will still be built, there are unlikely to be job losses at the Rosyth ship yards, close to Brown’s constituency. The JSF aircraft are being built in Fort Worth, Texas, with the involvement of BAE Systems.

The RAF, which had been due to replace its Tornado aircraft with the JSF, will now equip all its frontline squadrons with Eurofighter aircraft instead.

The Conservatives said any decision to axe a carrier would be “absolutely unacceptable” and typical of the government’s “chaotic, inconsistent and incompetent defence procurement policy”.

Liam Fox, the shadow defence secretary, said the move exposed the government’s claim that it wanted a completely independent strategic defence review. “The government is saying it is fully committed to the carriers while at the same time forcing them to be cut,” he said.

“It is confusing for the navy, it is confusing for industry and it is completely inconsistent with the whole concept of running an independent defence review.”

The Ministry of Defence said Bob Ainsworth, the defence secretary, remained 100% committed to the carriers but “financial circumstances mean some difficult decisions will have to be taken to prioritise our forces’ efforts in Afghanistan”.

The Royal Navy currently has three smaller 20,600-ton carriers: Illustrious, Ark Royal and Invincible. Illustrious is on a visit to Liverpool. Invincible has already been mothballed.

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