KGB double agent Oleg Gordievsky dead - defector was one of Britain's most valuable spies

KGB double agent Oleg Gordievsky, who defected to Britain in the 70s, has died aged 86. Gordievsky was regarded one of Britain's most valuable spies, providing vital information to the British Secret Intelligence Service from 1974 to 1985.

He died peacefully at his home in Surrey, the BBC reports. Counter-terrorism police are assisting the coroner, but his death is not being treated as suspicious. Gordievsky had been living in Surrey under police protection since 1985 after Moscow grew suspicious of him and exfiltrated him to the Soviet Union. He narrowly avoided arrest, trial and a firing squad by being smuggled across the border into Finland inside the boot of a car.

He joined the KGB in 1963, and was posted to the Soviet embassy in Copenhagen in 1966. But he soon became disillusioned by the system he was serving and began sending covert signals to Danish and British intelligence agents suggesting he might be willing to cooperate with them.

Gordievsky was especially outraged by the Soviet Union and its Warsaw Pact allies brutally crushing the Prague Spring in August 1968. In 1974, he agreed to pass secrets to MI6 under the codename Sunbeam.

He provided MI6 with invaluable intelligence about the Soviet Union, including insights into Mikhail Gorbachev's rise to power and the KGB's internal workings, which helped the West understand and manage relations with the Soviet bloc.

The spy also reularly met his MI6 handlers at a safe house in Bayswater, London where he was fed enough low-grade intelligence to keep Moscow happy. During the Cold War, Gordievsky worked as a KGB resident in London and warned his British handlers that the Soviet Union were preparing to strike first after becoming paranoid about a surprise attack by the West. The move led to NATO putting an end to the military exercise.

He was honoured by the Queen in 2007 with the Companion of the Most Distinguished Order of St Michael and St George. Gordievsky's defection was also hailed by then Foreign Secretary Sir Geoffrey Howe as "a very substantial coup for our security forces".

The following year, he was taken by ambulance from his "safe" Surrey home in November after an alleged plot to kill him. Gordievsky spent 34 hours unconscious and claimed he was poisoned with thallium by “rogue elements in Moscow”. While this was never proven, it led him to criticise MI6 for not looking after him properly.

He complained of partial paralysis and losing feeling in his fingers. And though tests found no evidence he had been given a suspicious substance, he said after his treatment at MI6's expense in Guildford Hospital: "I've known for some time I am on the assassination list of rogue elements in Moscow. It was obvious I'd been poisoned."

He later starred in the BBC series Secrets and Spies: A Nuclear Game, which delved into his incredible life.