The UK Royal Navy’s two aircraft carriers, HMS Queen Elizabeth and HMS Prince of Wales, will cost more and be ready much later than scheduled to provide less military capability, warns a report by a parliamentary watchdog.

The Public Accounts Committee (PAC) has revealed that the decision to fly the F-35 Joint Strike Fighters and adapting them to suit flight requirements on the carriers will not only increase the planes’ cost, but also that of the carriers.

The report said: "The technology proposed has yet to be tested and the [fighter] version the UK intends to buy will be unique to Britain. The costs of converting the carrier for use with the carrier-variant aircraft will not be known until 2012."

The UK Ministry of Defence has already reduced the number of Joint Strike Fighters it had planned to purchase; however, the carriers’ cost is likely to increase to £12bn.

According to the UK Government’s Strategic Defence Security Review 2010, the first carrier will be mothballed after its launch in 2016, while HMS Prince of Wales will be operational beyond schedule and is not expected until 2031.

The Guardian has quoted the former Labour minister and chair of the public accounts committee Margaret Hodge as saying: "There will be nine years without a carrier, and it will be at sea for fewer than 200 days on average."

Hodge added that cancelling both ships would have cost £2.4bn in compensation to BAE Systems, but would have resulted in £1.2bn in savings in the long term.