The government has not yet decided whether one of the Royal Navy's two aircraft carriers currently under construction will be mothballed, Defence Minister Peter Luff has told MPs.
As part of its strategic defence spending review (SDSR) in 2010, the government announced that it would reverse a Labour plan to buy Joint Strike Fighter F35-B jump jets and order instead the F35-C variant, which it said was able to travel greater distances and carry more weapons.
The cost of adapting the carriers to accommodate the different fighter planes was such that only one would become operational, ministers suggested at the time.
But at Commons questions on 11 June 2012, Conservative backbencher Julian Lewis asked the minister to "confirm that it is our intention" that both carriers would eventually come into use now that the government had decided to revert to Labour's original procurement plan.
"It will be a decision of the next SDSR as to whether both are operated or not," Mr Luff replied.
Labour MP Nick Smith urged the minister to give full details on how much the U-turn has cost.
The Daily Telegraph's estimate of £250m had been conservative, he said.
Mr Luff declined to give the full cost, but he said £40m had been spent on finding out how difficult it would be to convert the carriers.
"We don't think this money has been wasted," he said. "Changing the variant was considered the best course of action at the time of the SDSR, and these costs were necessarily incurred."