Admiral Sir Tony Radakin, who was appointed chief of the defence staff in October, said the undersea cables that transmit internet data are "the world's real information system".

Any attempt to damage them could be considered an "act of war", he added.

Sir Tony - a former head of the Royal Navy - told The Times newspaper there had been a "phenomenal increase in Russian submarine and underwater activity" in the last 20 years.

It meant Moscow could "put at risk and potentially exploit the world's real information system, which is undersea cables that go all around the world".

"That is where predominantly all the world's information and traffic travels," he added. "Russia has grown the capability to put at threat those undersea cables and potentially exploit those undersea cables."

The Royal Navy has been tracking Russian submarine activity during that period.

A collision between a British Type 23 frigate, HMS Northumberland, and a Russian sub has sparked wider speculation about the extent of Russian cable-mapping activity.

The collision, filmed in newly released footage by a documentary crew from Channel 5 working on a television series called Warship: Life At Sea, occurred in December 2020.

Sir Tony also said in his interview that the UK should develop hypersonic missiles to keep up with other nations doing the same.

UK in a weaker position

He said that because the UK does not have hypersonic arms and lacks the long-range capability that the Russians have got, the UK is in a weaker position.

"We haven't (got them) and we must have," he said.

Sir Tony also said he had provided ministers with Britain's "military choices" if Russia tries to invade Ukraine, but did not go into further details.

Defence Secretary Ben Wallace has said in the past it would be "highly unlikely" the UK would send troops if an invasion takes place, while The Times said cyber attacks were among the retaliatory actions being considered.

Talks next week

The US and NATO are scheduled to talk to Russia next week as a result of the tensions sparked by a Russian military build-up on the Ukraine border.

The talks come after Russia set out a series of guarantees it wants from NATO.

In the meantime, NATO general secretary Jens Stoltenberg said the alliance needs to prepare "for the possibility that diplomacy will fail".

Foreign Secretary Liz Truss has said any incursion into Ukraine by Russia would be a "massive strategic mistake" that would "come at a severe cost" to Moscow.