The British navy still doesn't have a grip on spiraling costs for an ambitious aircraft carrier expansion program, House of Commons lawmakers asserted this week.

A report issued Tuesday by the Commons Public Accounts Committee criticized the Ministry of Defense for continuing cost overruns in the program to build two new aircraft carriers and equip them with U.S.-built F-35B "jump-jet" joint strike fighters.

Committee members said the soaring costs have cast doubt on the government's ability to deliver the long-planned upgrades and puts it at serious risk.

The cross-party panel said it was "still not convinced that the Ministry of Defense has this program under control," adding the costly effort "remains subject to huge technical and commercial risks, with the potential for further uncontrolled growth in costs."

Margaret Hodge, the Labor Party member of Parliament who chairs the committee, pointed to a Defense Ministry decision in February 2012 to scrap plans to use F-35C fighters and instead revert to the original F-35Bs as an example of out-of-control spending.

"This U-turn, which will cost the taxpayer at least ($115 million), is the latest in an ongoing saga that has seen billions of pounds of taxpayers' money down the drain," she wrote.

"When this program 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 ($5.7 billion).

"We are now on course to spend ($8.5 billion) and have no aircraft carrier capability for nearly a decade."

Because of the situation, the lawmakers declared the 2007 contract signed by the previous Labor government for the carriers was no longer "fit for purpose" because there are not enough incentives for contractors to cut costs.

Ministers, meanwhile, said they are trying to juggle the need for state-of the-art technology with controlling costs, the BBC reported.

British Defense Secretary Philip Hammond told the broadcaster the Defense Ministry was negotiating with contractors to bring costs under control and praised the recognition the original contract was no longer sufficient to do so.

Under the massive program, Britain is constructing two carriers -- the Queen Elizabeth and the Prince of Wales. The biggest bone of contention has been the production costs of the aircraft that are due to fly from them, which could rise much further, the Financial Times reported.

Britain's National Audit Office determined this year the cost of the vertical-landing fighters has more than doubled since their development began 2001, with higher costs possible if orders don't reach expectations.

The Commons report also renewed fears delays in the development of the Crowsnest early warning radar system for the carriers means the vessels won't be equipped with the radar until two years after the first one is deployed in 2020.

But defense officials denied that, telling the newspaper the Crowsnest program will provide "an initial operating capability by the time the first carrier is in operational service."