Britain may be without a fully operational aircraft carrier until 2030, according to a report published by the Commons spending watchdog. The Public Accounts Committee (PAC) says two carriers being built will cost more, offer less military capability and be ready much later than planned.
It says the Royal Navy will be without a carrier until 2020, which may not be fully operational until 2030. The PAC also says the cost of scaling back the carriers is not fully known.
The committee said the adjustments made to the vessels meant just £600m cash savings and some costs would not be known for 12 months. The government says it expects to save £4.4bn over 10 years on the program.
The ships - HMS Queen Elizabeth and HMS Prince of Wales - were saved from defence cuts under the coalition government because, it said, it would cost more to cancel the projects than to proceed with them.
In last year's strategic defence review, ministers agreed to change the design of one, or both, of the aircraft carriers to make them compatible with the US Navy's version of the Joint Strike Fighter, rather than the short take-off, vertical-landing (STOVL) version that had been planned.
HMS Prince of Wales will not enter service - it will be built but not kitted out, and then kept as a reserve vessel - while HMS Queen Elizabeth is expected to go into service around 2020, with both said to cost £5.9bn.
The government says the two carriers were already £1.6bn over budget when it came to power - and says changes in the defence review reduced overall spending on the carrier strike program by £4.4bn over 10 years.
But the cross-party public accounts committee said the figure quoted for withdrawing the carriers and Harrier jump jets and converting one to use catapult and arrestor gear was actually £3.4bn - much of which was simply being deferred until after 2021.
The committee's Labour chairman Margaret Hodge said: While the department believes the decision will save £3.4bn, only £600m of this constitutes cash savings, with the other 80% simply deferred costs.
The report also says there is considerable uncertainty about the costs of modifying one of the carriers to accommodate a different type of fighter jet - and the full costs would not be known until December 2012.
While the change had reduced the technical risks associated with the STOVL aircraft - the fact that its full costs would not be known for another year left the project at risk of cost growth and slippage, the report said.
And it added there were other technical risks associated with integrating new aircraft with the carriers and suggested full carrier strike capability might not be achieved until 2030.
The committee said the Ministry of Defence had concentrated on immediate cash savings and short-term affordability, and did not focus strongly on long-term value for money.
Mrs Hodge said: Rather than two carriers, available from 2016 and 2018, at a cost of £3.65bn, we will now spend more than £6bn, get one operational carrier and have no aircraft carrier capability until 2020 - almost a decade.
Labour said the report showed there was a gaping hole in the government's credibility on defence.
Shadow defence secretary Jim Murphy said: It is high time ministers took responsibility for their actions. The rushed, Treasury-driven defence review left Britain without aircraft flying from an aircraft carrier for a decade.
But Defence Secretary Philip Hammond said the government was trying to get the MoD's finances back into balance having inherited a black hole from Labour.
He stressed the two aircraft carriers were already £1.6bn over budget when the coalition came to power - and said government spending cuts would save £4.4bn over 10 years on the carrier strike program.