The timing of the lack of available nuclear-powered attack submarines is not ideal, warn Military experts. Their unavailability has left the UK’s sub-sea internet and power cables at risk of sabotage by the Kremlin.

These particular subs are crucial in protecting the larger Vanguard submarines, which carry the bulk of the UK’s nuclear deterrent.

This comes following news that one of Britain’s flagship £3.5 billion aircraft carriers had broken down again, and is now being held in Norway for repairs.

Sir Richard Knighton, chief of the defence staff, has made comments that Russia has been “probing, challenging, testing our defences” and is “raising the stakes and risks crossing a line”.

He told the BBC: “I’m very clear that this is the most dangerous time I have known in my working life. The risks and threats to this country are greater than I have known since the Cold War.”

Lord West, former first sea lord and Labour security minister, added that it was “unacceptable” and “very worrying” that these subs are out of action.

He said: “The attack submarines are fundamental for looking after our ballistic missile submarines.”

“They are fundamental for frightening and terrifying the Russians.

“The fact that there has not been money invested in dry docks, in the maintenance facilities, in the men required to maintain and repair the submarines, in the spare parts for those submarines is why we have got to this position.

“It is just unacceptable and puts us in a very difficult position. If we haven’t even got an attack submarine available for use, then things are looking pretty bad.”

Defence analyst Francis Tusa, editor of the Defence Eye website, added: “It means that we no longer have a safe, sovereign nuclear deterrent.

“The first role of our hunter-killer submarines is to protect the Vanguard-class, the ballistic missile subs.

“Normally speaking, they leave the base at Faslane in Scotland one or two weeks ahead of the Vanguards and go out to sea and sweep the area to make sure there are no Russian subs. If we have no subs, we can’t do that.”