Filling the espionage ranks with legions of the non-belonging comes with its share of risk. The process is counter-intuitive, putting stock in skill and aptitude above the potential compromise of loyalty and divergence. Eventually, such a recruit might find a set of closely guarded principles.

The son of a Sephardic Jew and Dutch Protestant might well count as excellent material for British intelligence but George Behar ended up condemned in Britain and the toast of the now defunct Soviet Union. George Blake, as he came to be known, along with that other great British export of betrayal, Kim Philby, was always convinced that to authentically betray, you had to belong. That belonging came in loyalty to the Soviet Union. As Russian President Vladimir Putin declared solemnly on Blake’s passing this month, “The memory of this legendary person will be preserved forever in our hearts.”

The clandestine world of the Rotterdam-born Blake began early. He joined the Dutch resistance during World War II, serving as a courier after obtaining a set of forged papers. Under British instruction, he travelled through Brussels and Paris to unoccupied France, and made his way through neutral Spain, enduring a three-month period of imprisonment before making it to Britain via Gibraltar in January 1943. A spell with the Royal Naval Volunteer Reserve led to his enlistment into the ranks of British intelligence in 1944. There, he was charged with deciphering coded messages from the Dutch resistance.

After the war, his intelligence brief followed the pattern that would lead to his imminent conversion. He was tasked with keeping an eye on the Soviet forces in occupation of East Germany, a task he excelled at. He undertook courses in Russian at Cambridge. Then came the Communist states to the east: North Korea, the People’s Republic of China, and the Soviet Far East. Stationed in South Korea just before the outbreak of the Korean War in November 1948, he was given the herculean mission of creating networks within North Korea itself. In June 1950, he was captured by forces of the DPRK and interned with a coterie of diplomats and missionaries.

The internment period of 34 months proved critical. Blake claimed that his push towards the communist cause came during this time, a reaction to particularly brutal war methods, notably those used by the US Air Force. “It made me feel ashamed of belonging to these overpowering technical superior countries fighting against what seemed to be quite defenceless people.” The destruction of Korean villages, and a reading diet of Karl Marx, granted him alibis for the cause. “I felt it better for humanity if the communist system prevailed, that it would put an end to war.”

The credulous might think this to be the case, but Rebecca West, in her eminently interesting study of treachery in The Meaning of Treason, suggests a conversion during his time in the Dutch underground. Blake himself remained cryptic in his later days. “It is no longer of particular importance to me whether my motivations are generally understood or not,” he told the BBC’s Gordon Corera a decade before his death.

On his return to England in 1953 as a free man, Blake had already been recruited as a Soviet agent. His status as a full-blooded double agent was affirmed from his time in Berlin, where he was sent in 1955 with the mission of recruiting Soviet double agents.

For almost a decade Blake passed on information to his KGB handlers both bountiful and rich. According to a US estimate, 4,720 pages of documentary material made its way into Soviet hands between April 1953 and April 1961. It unmasked 40 MI6 agents in Eastern Europe. Highly placed agents working for Western agencies such as General Robert Bialek, Inspector General of the People’s Police in East Germany, were captured, suffering death or imprisonment.

Blake’s work also enabled the Soviets to score successes against the US Central Intelligence Agency. The late CIA case officer William Hood is convinced that Blake played a salient role in unmasking Peter Popov, an officer of the GRU, the Soviet Union’s military intelligence service and, it so happens, a CIA agent.

The greatest of blows, however, came in the exposure of the CIA Berlin Tunnel, which featured the tapping of three Soviet communications cables, an operation lasting 11 months and 11 days over 1955-6. Conducted jointly with British intelligence, Operation Gold involved the digging of a 1,476 feet tunnel six feet in diameter from West Berlin into the communist eastern sector of the city. Blake had foreknowledge of the tunnel, but a decision was made by the Soviets to prevent its initial exposure so as not to draw suspicion to their valuable mole. The discovery of the project was duly engineered as an accident; British and US intelligence were left out of pocket, furnished with a trove of useless disinformation.

Blake’s undoing came with the defection of Polish secret service officer, Michael Goleniewski. On his recall to London, he was arrested and pleaded guilty to five counts of passing information to the Soviet Union, breaching the Official Secrets Act. The case proved exceptional in a few respects. There was the severity of the sentence: 42 years. There was the breach of convention: the call made by the Lord Chief Justice Hubert Parker, to the then British Prime Minister Harold Macmillan to discuss the case. Even Macmillan was shocked by the decision. “The LCJ has passed a savage sentence – 42 years!” The Lord Chief Justice thought the time fitting, as Blake had, in his opinion, rendered much of the best efforts by British intelligence useless.

The sentencing came as a rude shock to Blake, having expected a term of 14 years. It also served to inspire support for his cause. “As a result, I found a lot of people who were willing to help me for the reason they thought it was inhuman.”

He would not be disappointed. In 1966, with the assistance of two anti-nuclear campaigners, Michael Randle and Pat Pottle, aided by Sean Burke, a colourful Irish petty criminal, Blake made his escape from London’s Wormwood Scrubs. Both Bourke and Blake were smuggled out of Britain and to East Germany. Blake’s final destination would be the Soviet Union, where a colonel’s rank with the KGB, awards and belonging awaited.

The British establishment was left reeling. Randle and Pottle went on to justify their actions to save Blake from a sentence “vicious and indefensible, reflecting no credit on British justice but rather the obsessions of the Cold War, and the hypocrisy and double standards over espionage by ‘our’ side and ‘theirs’.” To have spied for the Soviet Union was “no more reprehensible, morally or politically, than much of the activity of Western Intelligence Agencies.”

One CIA note on Blake’s escape is sour. “The facts of the escape demonstrated beyond doubt that it was engineered by the Soviets. The buoying effect upon the morale of Soviet spies everywhere can be easily imagined.” Once in the business of espionage, everything must have a sinister design, an architectural base upon which to reap success and failure. One could always blame those other worthy agents of history, incompetence and complacence. The journalist Philip Knightley, an accomplished student on the subject of espionage, points to a third: opportunity.

The exploits of the Cambridge set – Anthony Blunt, Guy Burgess, Donald Maclean, John Cairncross and Philby – soiled British intelligence. But Blake proved more devastating than all of them, though measuring that contribution is a near impossible task. Britain’s secret services, as Andrew Boyle concludes, were embarrassed for both the harsh judicial sentence against Blake and the fact that his case “made, and still makes, the SIS the laughing-stock of the world.” The skilled spy outwitted the SIS and CIA; the KGB gave him deserved recognition. Had it not been for Blake’s own confession – the SIS having authorised him to maintain close connections with the Soviets – he might never have been nabbed.