The sum is needed to honour ministers’ commitment to build or buy three logistic ships, eight Type 26 Global Combat ships, new mechanised infantry vehicles and nine Boeing P-8A Maritime Patrol aircraft.

But a new report claims the cost will not be covered by £178billion of defence spending over the next 10 years pledged by the Government.

First Sea Lord Admiral Sir Philip Jones has appointed the head of the Royal Marines, Major General Rob McGowan, to fight Treasury mandarins for the extra money.

The choice of Maj Gen McGowan is significant as the Royal Marines stand to lose more than 1,500 troops as part of the ongoing National Security and Capability Review. 

Based in Portsmouth, he will head a 20-strong team to persuade the Treasury to detach the cost of replacing the Trident nuclear deterrent from the defence budget and halt the scuttling of two Royal Navy amphibious landing vessels.

In a letter to Royal Marines staff, he wrote: “I want to reassure you all that I am personally engaged in this review process and we have some of our best people working on it.”

Of the £178billion committed by the Government over the next decade, £82billion will pay for new equipment and £23.4billion on support arrangements for it.

A further £67.2billion will go to support existing in-service kit while £5.4billion will be retained to cover contingencies.

However, the report from MPs on the defence select committee, titled Gambling on Efficiency: Defence, Acquisition and Procurement, casts serious doubts on the Ministry of Defence’s ability to keep its promises.

It states that ability to design, build or buy the logistic ships, combat ships, infantry vehicles and maritime patrol aircraft rests on achieving a further £9.8billion in savings.

The MoD has set out £14.4billion in overall efficiency savings – £7.1billion was announced before 2015 and a further £7.3billion more recently. However, defence chiefs only managed to achieve £4.6billion in savings from the first target.

Committee chairman Dr Julian Lewis MP said: “It is extremely doubtful that the MoD can generate even more efficiencies from within its already stretched budget on the scale required to deliver its equipment plan.

“This will mean reducing the number of ships, aircraft and vehicles planned. The only alternative would be to fill the gap with new Treasury money.”

The MPs’ report added: “Even if all the efficiencies are realised, there will be little room for manoeuvre in the absence of sufficient headroom and contingency funding. 

“This is not an adequate basis for deleting major projects at the heart of the UK’s defence capability.”

Last night General Lord Dannatt, former head of the British Army, urged a full audit, in the form of a new Strategic Defence and Security Review.

He said: “This is the only way to set out the result of the capability study against what our defence policy ambitions are, and we need one quickly.

"That’s when the real discussion with the Treasury begins.

“Do we want to retain our global footprint, our ability to help allies, our status in the P5 [permanent members of the UN Security Council], or do we want to become a small insignificant island off the coast of Europe?”

An MoD spokesman said the equipment plan “continues to deliver the cutting-edge kit to keep the UK safe. We are making good progress towards our efficiency target”.