Ministers set to recommend downgrading of aircraft carrier jets

• Ministers set to recommend today that carriers are equipped with the F35B jump jet variant of the American built Joint Strike Fighter (JSF)

• It would mean reversing a decision in the coalition government’s 2010 Strategic Defence and Security Review to switch to the more capable F35C carrier version.

The F35C has a longer range and carries a bigger payload, as well as being inter-operable with US and French forces.

The cost of fitting the necessary catapults and arrestor gear - “cats and traps” - to one of the carriers, while the other ship is mothballed, has since spiralled to a reported £1.8 billion.

An announcement had been expected before Easter, but giving evidence to the Commons Public Accounts Committee, MoD Permanent Secretary Ursula Brennan said a decision had yet to be finalised.

“Ministers have not made a decision. The Secretary of State for Defence (Philip Hammond) wanted to take the time to assure himself about these issues,” she said.

“He has been asking us a lot of detailed questions. He then has some discussions he needs to have with his ministerial colleagues, including the National Security Council.”

During questions by MPs, Ms Brennan repeatedly refused to say how much had been spent so far on conversion work to fit the cats and traps.

“The expenditure around that further work is the subject of discussion with ministers,” she said. “This is work ministers need to reach a view on.”

Committee chairman Margaret Hodge said the decision to switch to the F35C had been taken “without a proper understanding of the costs and risks” and she criticised Ms Brennan for failing to restrain ministers.

“Why on earth don’t you exercise a little bit of your accounting officer authority and issue letters of direction to stop ministers taking decisions which end up with the taxpayer having to foot the bill for a massive amount of billions of pounds of torn up notes?” she said.