MARGARET THATCHER ordered the Royal Navy to land Special Boat Service (SBS) frogmen on the coast of Sweden from British submarines pretending to be Soviet vessels, a new book has claimed.

The deception involved numerous incursions by British forces into Swedish territorial waters in the 1980s and early 1990s, designed to heighten the impression around the world of the Soviet Union as an aggressive superpower.

Sometimes the boats landed commandos, but often their job was to fool the Swedes by mimicking the sonar signals given off by the Soviet vessels that stalked the same waters.

The Swedish government, neutral in the cold war, is not believed to have known about the deceptions, which were carried out by the British and American navies.

A Swedish parliamentary inquiry noted evidence found on the seabed of submarine “midgets with bottom-crawling capacity of a hitherto unknown character”.

The cold war under the Baltic is detailed in a book by Ola Tunander, research professor at the International Peace Research Institute, Oslo.

Tunander writes that there were more than 4,000 reported detections of foreign submarines in Swedish waters in 1982-92. The West claimed the vessels were all Soviet, probing the country’s defences. Tunander believes many were part of a CIA-run operation by Britain and America that continued until the collapse of the Soviet Union.

“A lot of cold war intelligence operations were failures, but this one was a real success,” Tunander said.

He reached his conclusions after speaking to former Royal Navy submariners and CIA officials. One British naval captain told him: “Margaret Thatcher signed approval for every single operation.”

One of the boats used was HMS Orpheus, a submarine kitted out for SBS operations.

Tunander said he had once sat next to a British admiral at dinner and questioned him about the operation. He replied that it was “none of my business”, Tunander said. “The admiral then added jokingly, ‘Don’t people fall under buses sometimes?’ ” This weekend Sir Keith Speed, navy minister from 1979 to 1981, was asked if the missions had happened. He replied, “Yes,” but added: “I cannot say any more as I am bound by the Official Secrets Act until the day I die.”

Russian and Nato submarines were involved in some of the most aggressive clashes of the cold war as the Soviet Union examined the potential for controlling Scandinavia. This would have allowed it to outflank Nato armies in Germany and threaten Atlantic shipping.

The confrontation under Swedish waters came to light in 1981 when a Soviet Whiskey class submarine ran aground in an incident called “Whiskey on the Rocks”.

As late as 1988 Ingvar Carlsson, the Swedish prime minister, warned the USSR: “Blood will flow. We will use all available methods . . . to sink the submarines . . . Our borders are holy.”

A senior Swedish source said the submarine incidents had been fully investigated and that Tunander’s claims were “completely untrue”.

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