THE Ministry of Defence has been accused of “terrifying incompetence” following reports that Britain's entire fleet of attack submarines is currently out of operation due to repair and maintenance work.

It is claimed that seven nuclear-powered vessels, including three new Astute class submarines, which cost more than £1 billion each, and four Trafalgar class boats are all currently classed as non-operational.

The UK's Vanguard submarines, which carry Trident nuclear missiles, are in operation but according to The Sun it is the first time in decades the Royal Navy has no attack submarines ready.

Five of the submarines are having refits or maintenance after breaking down while HMS Ambush has been recalled home for repairs after colliding with a merchant vessel in Gibraltar.

The remaining attack submarine, HMS Astute, is having trials at sea following maintenance work and is weeks away from being operational for missions, according to the report.

One claim is that defence chiefs kept the news from Theresa May because they “fear her reaction”.

A Royal Navy spokesman said: "We don't comment on specific submarine operations. Britain has a world-class fleet. The Royal Navy continues to meet all of its operational tasking, deploying globally on operations and protecting our national interests as Britain steps up around the world."

Last month, it was revealed that a test firing of a Trident missile by the Royal Navy off the coast of America last June had allegedly failed.

Last week, Sir Michael Fallon, the Defence Secretary, told The Herald: “Secrecy is part of the deterrent. The deterrent's credibility obviously depends on us keeping its operation as secure as possible."

He added: “There are some things that people have to trust the Government on and the nuclear deterrent is one of them. But, let me just reassure you, that we would not have asked Parliament to renew the submarine fleet if we had had any doubts about the safety, capability or effectiveness of the deterrent."

However, responding to the latest reports, Brendan O’Hara, the SNP’s defence spokesman, said: "They are quite astonishing, and if - as reported - the entire UK fleet of attack submarines was out of action and the MoD ‘kept it from the Prime Minister’ that it is simply indefensible.

"First the recent Trident malfunction fiasco, now this. How can we possibly trust these people when we hear about this terrifying incompetence followed by yet another Whitehall nuclear cover-up?"

The Astute class vessels are the most powerful attack submarines ever operated by the Royal Navy.

They weigh around 7,400 tonnes, equivalent to nearly 1,000 double-decker buses, and are 328 feet long.

Armed with Tomahawk cruise missiles, the Barrow-built vessels can accurately strike targets up to 1,200 miles from the coast.

Advanced stealth technology means they can remain undetected despite being 50 per cent larger than the Trafalgar class submarines they will replace.

Their nuclear reactors will not need refuelling in their entire 25-year life and they make their own air and water, enabling them to circumnavigate the globe without needing to surface.