A Russian spy ship is said to have stopped at sites off the Norfolk coast while disguised as a scientific research vessel, as part of plans to sabotage key energy infrastructure.

The Admiral Vladimirsky is officially designated as an expeditionary oceanographic ship, or underwater research vessel.

But according to a joint investigation by broadcasters in Denmark, Sweden, Finland and Norway it is a Russian spy ship which has been gathering intelligence in the North Sea in preparation for a possible conflict with the West.

Experts say the vessel carries underwater surveillance equipment and is mapping key sites - such as wind farms and communication cables - for possible sabotage.

Eastern Daily Press: Scroby Sands Wind Farm off Great YarmouthScroby Sands Wind Farm off Great Yarmouth (Image: Mike Page)

According to the investigation, the ship sailed around the Baltic and North Seas for a month, passing the sites of current and future wind farms off the coast of several Scandinavian countries, as well as Britain and the Netherlands.

Its voyage was tracked, and records show the ship sailing south through the North Sea, passing close to the Norfolk coast, before turning around off Essex and heading back through the same area.

The records show the vessel slowed down when it approached areas where there are wind farms and loitered there.

During its voyage, it had its transmitter turned off, in an attempt to conceal its location.

The waters off the Norfolk coast already have some of the country's densest concentrations of wind farms, and there are projects under way to build even more.

One of the farms under development is predicted to supply more than 10pc of the UK domestic energy, once completed.

Norfolk waters are also crossed by crucial communication cables and gas pipelines, which come ashore at Bacton.

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The team behind the investigation believes the Admiral Vladimirsky is part of a fleet of Russian espionage ships - disguised as fishing trawlers and research vessels - examining key sites to sabotage, in the event of the war in Ukraine escalating into a wider conflict with the West.

Danish broadcaster DR has published a video of an encounter at sea between a small boat carrying its investigative team and the Russian ship, filmed off the Danish coast in November.

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It shows a man, wearing a balaclava and military gear and carrying an assault rifle, appearing on the deck of the Admiral Vladimirsky.

The ship is thought to have entered the Moray Firth, off the coast of Scotland, on November 10 last year.

Eastern Daily Press: Sheringham Shoal Offshore Wind FarmSheringham Shoal Offshore Wind Farm (Image: Newsquest)

Experts have previously warned about the vulnerability of Britain's offshore infrastructure.

In October last year police declared a major incident in the Shetland Islands after an underwater cable was cut.

The incident severely hampered communications with the mainland and was blamed at the time as having been probably caused by "fishing vessels".

Cables are regularly cut by accident and no evidence has emerged to indicate that the Shetland incident was a result of hostile activity.

However, there has been one major act of underwater sabotage since the Russian invasion of Ukraine.

Last September, parts of the Nord Stream pipeline, designed to carry gas from Russia to Europe under the Baltic Sea, were bombed.

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At the time, many accused Russia of being responsible but since then other reports have suggested other possibilities, including pro-Ukrainian agents. Investigations are ongoing.

Chairman of the commons defence committee Tobias Ellwood, told the Telegraph that the findings of the latest investigation underlined the need for the UK to expand its armed forces.

“We simply can no longer protect our near seas and, rightly, step forward further afield, with our current peacetime-sized Navy, Army and Air Force,” he said.

An MoD spokesman said: “We increased Royal Navy presence patrols after the Nord Stream incident and have invested £65 million in the first of our two Multi-Role Ocean Surveillance ships.”