Media playback is unsupported on your device Media caption Jonathan Beale sees the new carrier taking shape in Rosyth

MPs have raised fresh concerns about the cost of fighter jets for the Royal Navy's new aircraft carriers, warning of "uncontrolled growth" in budgets.

The Commons Public Accounts Committee said billions of pounds had already gone "down the drain" during the carrier strike procurement programme.

An order for jump jets for the two new carriers was scrapped in 2010, only to be reversed 18 months later.

Ministers said they were negotiating to bring costs under control.

The Labour government signed a contract for two new aircraft carrier in 2007.

Aircraft switch

The cross-party committee - which assesses value for money in government spending - said it still regarded the project as "a huge technical and commercial risk" and was not convinced the Ministry of Defence had it under control.

Expected to cost £3.65bn when it was approved six years ago, this was now on course to rise to £5.5bn, it said in its report.

The Labour government placed orders for two carriers to be equipped with the F-35B variant of the US-built joint strike fighter (JSF), which is capable of short take-off and vertical landing.

In its 2010 Strategic Defence and Security Review, the coalition changed to the F-35C version, which has a longer range and can carry more weapons.

But it announced a U-turn in February last year, reverting to the original aircraft for logistical and financial reasons.

The National Audit Office has warned that this change of mind will cost taxpayers £74m.

In its report, the committee said officials had made basic errors, such as failing to factor in the cost of inflation and VAT.

"This U-turn is the latest in an ongoing saga that has seen billions of pounds of taxpayers' money down the drain," its chairman Margaret Hodge, a Labour MP, said.

'Extended readiness'

The committee also suggested that Labour's overall contract was not "fit for purpose" as there were not enough incentives for contractors to cut costs.

Assembly work is continuing on one aircraft carrier - HMS Queen Elizabeth - but it will not be finished until 2016 at the earliest.

The construction of the other - HMS Prince of Wales - will overlap and the current plan is for one of them to be operational while the other is kept in "extended readiness".

The committee's report cast doubt on the MoD's claim that the new carrier-based strike force would be fully operational by 2020.

Following the retirement of HMS Invincible and HMS Ark Royal, the UK only has one aircraft carrier - HMS Illustrious - at its disposal and this cannot be used by strike aircraft, only helicopters - leading to warnings of a decade-long capability gap.

Defence Secretary Philip Hammond said he welcomed the committee's finding that the contract signed by Labour had not been "fit for purpose".

He added: "We are currently negotiating with industry to seek to secure proper alignment between industry and the MoD over the balance of the project and so bring the costs under control, but we are doing so within the context of a contract that gives us very little negotiating leverage.

"As the National Audit Office recognised in their report in May, the MoD acted swiftly to switch back to short-take-off-vertical-landing aircraft as soon as it became clear that the alternative would cost more money.

"In doing so, we did incur some costs, as the PAC records, of £74m - but we did so in order to save £1.2bn, a clear demonstration of our commitment to safeguard taxpayers' money."

For Labour, shadow armed forces minister Kevan Jones said: "The chaos of the government's carrier U-turn gets worse and worse.

"Having announced this triumphantly, David Cameron has cost the taxpayer millions of pounds and has left the country without aircraft on an aircraft carrier for a decade. When defence budgets are tight, this looks incompetent and wasteful."