The price for the new carriers will increase between $1.7 billion and more than $3 billion because of the British government's decision to make them fit for launching the Lockheed Martin F-35 Lightning II, also called Joint Strike Fighter, the BBC reports.
The carriers are to be outfitted with catapults and traps to accommodate the naval version of the JSF instead of the more expensive vertical takeoff and landing version London initially planned to buy.
Converting one or both carriers to accommodate the cheaper JSF will drive down operational costs and enhance the vessels' capability and interoperability with Britain's NATO allies, a spokesman for Britain's Defense Ministry told the BBC.
Built by a consortium including BAE Systems and Babcock International from Britain as well as France's Thales, the two carriers would now cost a total of $11.7 billion, the BBC says -- more than the $8.7 billion announced by London last fall and a far cry from the $6.5 billion disclosed at the contract signing in July 2008.
London didn't want to confirm those numbers.
"Final costs are yet to be agreed and detailed work is ongoing. We expect to take firm decisions in late 2012," the Defense Ministry spokesman told the BBC.
The carriers have been controversial because of their high costs at times of budget austerity.
BAE Systems had pleaded with the government not to scrap the carrier program, citing the loss of jobs and high costs linked to such a move.
The government last October decided that it would build both carriers with the first, the HMS Queen Elizabeth, to enter service with the British navy. Once the second carrier, the HMS Prince of Wales, is built, it is to be mothballed or sold to a third country.
The announcement was made as part of the country's first strategic defense review in more than a decade. British Prime Minister David Cameron said his government would cut defense spending by 8 percent, reduce troop numbers by 17,000 to 158,500, scrap defense equipment such as airplanes, tanks and artillery and ax 25,000 civilian jobs in the Defense Ministry.