Former KGB double agent Oleg Gordievsky has died aged 86.

Gordievsky, considered the most valuable spy for Britain within Russian intelligence agencies, spent many years providing crucial information to both MI6 and MI5.

He passed away 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 has lived in Surrey under police protection since Moscow became suspicious of him in 1985.

He narrowly escaped arrest, trial and a firing squad by getting smuggled across the border into Finland in the boot of a car.

Before becoming a spy Gordievsky had been languishing in a desk job at headquarters in Moscow for three years.

And so, when the plum job of a posting to the KGB station in London came up in 1981, he seized the opportunity. 

KGB double agent Oleg Gordievsky has died aged 86

He spent many years working as a double agent, passing vital intelligence to both Britain’s MI6 and MI5

Since 1985, Gordievsky has resided in a ceremonial county under police protection due to growing suspicions from Moscow. He narrowly escaped arrest, trial, and a firing squad by being smuggled across the border into Finland hidden in a car’s trunk.

Gordievsky worked undercover for the KGB – the Soviet secret service – in London in the early Eighties, sending reports back to Moscow. 

But he was also, bravely, spying for the West. 

The London rezidentura was one of the most active in the world, and he would be handling secrets of the first importance.

He pretended to be enthusiastic, servile, and falsely humble towards his boss, known as The Crocodile, a very unpleasant individual whom Gordievsky despised.

But his toadying worked. He was appointed to the Soviet embassy in London, ostensibly to the diplomatic position of Counsellor but in reality deputy head of the KGB station housed there.

One by one, Gordievsky exorcised the demons of MI6 history.

For years there had been rumours of a ‘Fifth Man’, an unexposed member of the notorious Cambridge spy ring of Burgess, Maclean, Philby and Blunt. Gordievsky confirmed it was John Cairncross, a former MI6 officer.

Pictured: Oleg Gordievsky is made a Companion of the Order of Saint Michael and St George by The Queen at Buckingham Palace

Pictured: KGB and MI5 Double agent Oleg Gordievsky (left) and codebreaker Alan Stripp pit their wits over the Mastermind

He was able to name a Soviet spy discovered in 1946 but never formally identified, as Leo Long, a former intelligence officer, and that an Italian nuclear physicist, Bruno Pontecorvo, who worked on Britain’s wartime atomic bomb research, had volunteered his services to the KGB seven years before he defected to the USSR in 1950.

He also laid to rest the long-held conspiracy theory – on which much angst had been expended in the intelligence services – that Roger Hollis, a former chief of MI5, was a Soviet mole.

Most importantly, Gordievsky also put to rest MI6’s anxiety about current operations. 

MI6 had expected to learn that there was a vast network of KGB agents in Britain, communist spies like the Cambridge Five who had wormed their way into the Establishment to destroy it from within.

But Gordievsky told them that the KGB had only a small handful of agents, contacts and illegals in Britain, none very threatening.

Moreover, his insider’s depiction of KGB operations indicated that MI6’s Soviet adversary was not the invincible giant of myth, but flawed, clumsy and inefficient. It remained vast, well-funded and ruthless but its ranks included many time-servers, boot-lickers and lazy careerists with little imagination.

The KGB was still a dangerous antagonist, but its vulnerabilities and deficiencies were now exposed. It could be beaten.

This is a breaking news story, more to follow.