Vladimir Putin is poised to unleash a fleet of submarines that could cripple the UK’s internet and natural gas infrastructure, the head of the Royal Navy has warned.

General Sir Gwyn Jenkins, who serves as the first sea lord, warned that the Kremlin was pouring rubles into a research team Britain could not afford to ignore, and whose underwater capabilities were “improving all the time”.

He warned that the unit, the Main Directorate of Deep-Sea Research (GUGI), was behind plans to map out and potentially sabotage sea-bed infrastructure.

That includes internet cables and gas pipelines, both of which the UK and NATO rely on for communications and key power supplies.

“We’ve seen GUGI’s subsurface capabilities restarting,” the first sea lord warned in an interview with the Financial Times. He indeed: “We know that they’ve had some issues with that programme. It appears that they have reset that programme. So we’re expecting them to deploy again.”

The navy chief said the GUGIs ability to operate submarines and extreme depths was giving the Kremlin the “option for physical action, if they want it”.

GUGI has not carried out underwater missions for decades, but its actions are classified. Until recently, it was reported, UK naval chiefs have refused to acknowledge it exists, or even discuss what they know of its activities.

Back in 2019, 14 of the Russian unit’s senior officers died in a fire on one of its submarines, the Losharik, which had been undertaking an operation just off the eastern coastline of Norway.

The Financial Times exposed some of what the unit could do earlier this year, after an investigation showed that the Russian spy ship, Yantar, had been near the cables which connected the UK and Ireland.

Yantar, called a “research” ship by the Kremlin, can unleash mini-submarines that can dive down six kilometers.

The first sea lord, who took the top job this year, did not comment on what “physical action” GUGI could undertake.

Naval experts, however, have said that Moscow could use the unit to planet explosives at key notes where cables meet under the water.

Jenkins told the FT: “You have an aggressive regime with an acknowledged capability, an acknowledged desire to implement sabotage and transition towards points of tension, and you have a facility that enables them to go to depths with submersibles on mapped infrastructure that is sensitive to us.”

He added: “That doesn’t seem like a good combination to me.”

It was reported that the Kremlin has continued to invest in the group, despite the rising costs of the war in Ukraine.

The Royal Navy has taken steps to counteract the threat, which has included a new defence agreement with Norway, a key ally in monitoring Russian ships and submarines that enter European waters.

It’s also spending £4million for a ring of sensors and automatic vessels known as the “Atlantic Bastion”, which is getting another £35million this year, should a deal be reached between the MoD and the Treasury.

Jenkins said it was important to protect the UK from the submarine force, and the conventional forces of Russia’s large Northern Fleet.

“We effectively . . . do have a border with Russia. It’s the open seas to our north, and any complacency that somehow we have eastern Europe between us and that threat is a misplaced complacency,” he said.

“The Russians continue to invest in these [naval] capabilities, and they’re improving all the time . . . we should take that threat very seriously, because the comfort that we take from being an island that is separated from continental Europe is a false comfort,” added Jenkins.

In the interview, he warned that “We are living in a new era of threat which is less predictable and more dangerous” and cautioned “the threat that Russia poses to our nation” was growing as they “are mapping our undersea cables, our networks and our pipelines – and those of our allies.”