Russia has a programme to sabotage wind farms and communication cables in the North Sea, according to new allegations.
The details come from a joint investigation by public broadcasters in Denmark, Norway, Sweden and Finland.
It says Russia has a fleet of vessels disguised as fishing trawlers and research vessels in the North Sea.
They carry underwater surveillance equipment and are mapping key sites for possible sabotage.
The BBC understands that UK officials are aware of Russian vessels moving around UK waters as part of the programme.
The first of a series of reports is due to be broadcast on Wednesday by DR in Denmark, NRK in Norway, SVT in Sweden and Yle in Finland.
A Danish counter-intelligence officer says the sabotage plans are being prepared in case of a full conflict with the West while the head of Norwegian intelligence told the broadcasters the programme was considered highly important for Russia and controlled directly from Moscow.
The broadcasters say they have analysed intercepted Russian communications which indicate so-called ghost ships sailing in Nordic waters which have turned off the transmitters so as not to reveal their locations.
The report focuses on a Russian vessel called the Admiral Vladimirsky. Officially, this is an Expeditionary Oceanographic Ship, or underwater research vessel. But the report alleges that it is in fact a Russian spy ship.
The documentary uses an anonymous former UK Royal Navy expert to track the movements of the vessel in the vicinity of seven wind farms off the coast of the UK and the Netherlands on one mission.
It says the vessel slows down when it approaches areas where there are wind farms and loiters in the area. It says it sailed for a month with its transmitter turned off.
When a reporter approached the ship on a small boat, he was confronted by a masked individual carrying what appeared to be a military assault rifle.
The same ship was reportedly sighted off the Scottish coast last year. It was spotted entering the Moray Firth on 10 November and seen about 30 nautical miles east of Lossiemouth, home to the RAF’s Maritime Patrol Aircraft fleet before heading slowly west.
The BBC understands that UK officials are aware of Russian intent to conduct what is known as undersea mapping, including using boats that move around in UK waters.
If there are specific threats against the UK these would be investigated, but sources declined to say what activity might have been looked at so far.
