MPs are to probe the spiralling cost of the aircraft carriers being built on the Clyde after it emerged that the bill has almost doubled.

The Coalition Government is expected to confirm soon that the final total will top £6 billion.

Labour accused Defence ­Secretary Philip Hammond of a "shambles" and said claims he had balanced the books in his department looked "increasingly nonsensical".

But Coalition sources hit back saying they had now successfully reformed the controversial Labour-signed contract to build the carriers.

Ministers believe they will soon have a deal that will ensure industry bears the brunt of future cost increases.

Margaret Hodge, the Labour chairwoman of the Public Accounts Committee, described the latest price hike as "disappointing" as she indicated her committee would look into the rising costs.

She added that ministers had said for years they were improving control over major projects "but this gives lie to that assertion".

The overall cost of aircraft carriers is expected to rise by £800 million to £6.2 billion.

The two massive vessels were originally priced at £3.5 billion by the then Labour government in 2007.

But the project has long been dogged by controversy.

In 2010 the newly elected ­Coalition Government was furious when it emerged that it would be more expensive to scrap the carriers than to build them.

Ministers reluctantly went ahead with the project, but faced more negative headlines when they announced that one vessel would be mothballed immediately after it was completed.

Coalition ministers have also twice changed the type of aircraft that will fly from the carriers.

Last month it was revealed that Ministry of Defence (MoD) officials were given just hours to pull together botched plans to change the design to accommodate a new plane.

Bernard Gray, chief of defence matériel at the MoD, said civil servants were told to calculate the costs "by five o'clock" because they were wanted by some of "the most senior people in the country".

Coalition ministers ploughed ahead with the changes but were eventually forced into a humiliating U-turn, costing taxpayers around £100m.

In September, MPs on Mrs Hodge's committee issued a scathing warning that the multi-billion-pound contract was "not fit for purpose".

The PAC warned the costs could still spiral as industry had no incentive to keep them down.

The project itself also remained "high risk" with unresolved technical problems creating the potential for "uncontrolled growth" in the final bill, they said.

The committee also warned that in the three years they had been in power the Tory-LibDem Coalition Government had yet to complete " crucial negotiations" with industry over the carriers.

Last night Vernon Coaker, Labour's Shadow Defence Secretary, accused ministers of botching major projects.

"This is the latest in a series of financial fiascos in the MoD under David Cameron," he said.

"The Government needs to come clean about the cost of the aircraft carrier programme and explain what has caused an increase that leaves the total projected cost at £6.2bn, almost double what was originally envisaged."

He added: "The Defence ­Secretary's claim that he has balanced the MoD books looks increasingly nonsensical."

Mr Hammond told MPs last night: "Negotiations with the Aircraft Carrier Alliance are ongoing, but we believe they are close to reaching a conclusion."

He said he would update them "as soon as we have information to convey".