British spy bosses repeatedly tried to protect Soviet double agent Kim Philby because they believed he "couldn't possibly be a traitor", according to a new book which was banned by MI6.

Tim Milne, an MI6 spy who was Philby's oldest friend, has revealed the extraordinary lengths to which intelligence officials went in order to protect the notorious figure.

Philby came under suspicion when two other members of the Cambridge spy ring fled to Moscow - but despite a 12-year investigation, he was never brought to justice and was eventually allowed to defect to the USSR himself.
MI6 chiefs refused to believe that he could be guilty because of his apparently distinguished service and Establishment background, and shielded him from an MI5 probe....

Milne reveals in his book that Elliott - who believed Philby when he said he had stopped spying for the KGB 16 years earlier - made several blunders in the questioning which allowed the double agent to walk free yet again.

Elliott's recording of the interrogation was inaudible because of the noise of traffic outside, and he allowed Philby not to sign a statement in which he admitted his guilt, instead saying he would return for another meeting later.

Before that meeting took place, Philby vanished in January 1963 and settled in Moscow, where he lived for 25 years before his death.

MI6 officials continued to insist that he had given them valuable information about other agents, according to Milne, even telling Harold Macmillan that he had helped detect Soviet spies in Britain.

The security services tried to block the appearance of Milne's book, but after he died in 2010 his family continued the fight against censorship, and this week it will be published by Biteback Publishing.

A book by Kim Philby's closest friend inside MI6, once banned by intelligence chiefs but due to be published this week, explains one of the most enduring mysteries surrounding the notorious Soviet spy – how, despite growing evidence of his treachery, he was regarded as an innocent and loyal colleague.

Tim Milne, a former MI6 officer – and nephew of the author of the Winnie the Pooh books – describes in Kim Philby: The Unknown Story of the KGB's Master Spy how for 12 years his colleagues went to extraordinary lengths to block an MI5 investigation into the man who was eventually exposed as the key member of the Cambridge spy ring.

When Donald Maclean and Guy Burgess, two other members of the Cambridge spy ring, fled to Moscow, MI5's suspicion that Philby was the "third man" who tipped them off forced him to resign, but even after this Philby continued to be robustly defended by MI6 officers.

"Even then the general (MI6) office belief was that he'd had to go simply to preserve good relations with the Americans," Milne writes. He adds: "There very few people in the service who had inspired so much trust and respect as Kim, and so much affection among those who had worked closely with him."

Philby's charm fooled those at the very top of MI6, Milne shows. Sir Stewart Menzies, the wartime head of MI6, believed Philby was a patriotic intelligence officer and victim of an MI5 witch hunt. Philby "couldn't possibly be a traitor", Menzies privately told Sir Dick White, the head of MI5.

When MI6 chiefs were finally forced to succumb to mounting evidence that Philby had indeed spied for the Moscow, to avoid embarrassment and political scandal – and, not least, American fury – Philby was offered immunity from prosecution and publicity in return for a confession.

But MI6 blocked a plan to send a tough MI5 interrogator, Arthur Martin, to question Philby in Beirut – where MI6 had helped to secure him the post of correspondent for the Observer newspaper – and instead sent one of Philby's former MI6 colleagues, Nicholas Elliott.

Elliott believed Philby's untruthful claim that he gave up spying for the Soviet Union as early as 1946. Elliott allowed Philby to write his own two-page "confession" but failed even to ensure that Philby signed it, according to documents recently released at the National Archives and reproduced in Milne's book. Though the interview was recorded, Elliott left the window open and the noise of traffic outside drowned out much of what was said.

Such was Elliott's trust in Philby that he sought his advice about other members of the Cambridge spy ring, including Anthony Blunt and John Cairncross, who had come under suspicion because of their friendship with Burgess but were protected by Philby before being exposed years later.

Elliott urged Philby to return to Britain. Though Elliott may have appeared sympathetic, Philby clearly believed MI5 would eventually confront him with hard evidence. He jumped aboard a Russian ship in Beirut in January 1963.

Yet MI6 still clung to the view that somehow Philby, despite his treachery, was someone who could be trusted, Milne says. In a briefing for the prime minister, Harold Macmillan, included in Milne's book, MI6 officers insisted that Philby had been helpful and cleared up suspicions about a number of Soviet spies.

Tim Milne was Philby’s closest associate in the Secret Intelligence Service, MI6. A fellow pupil at Westminster, he was recruited into the secret world during the Second World War on the recommendation of his friend. In retirement, he wrote a memoir of his friendship with Philby, which was promptly banned from publication by MI6. Now, four years after Milne’s death at the age of 97, his story can be told.

Kim Philby: The Unknown Story of the KGB’s Master Spy is an often-intimate portrait of the Third Man, candid in its assessments. Written without rancour – despite Philby’s attempt to blacken Milne’s name during interrogation – it charts the 37 years from first meeting at Westminster in 1925 to Philby’s escape from Lebanon to Russia.

The book has been updated with extracts from freshly released official files showing how Philby continued to deceive even after confessing his treachery. From 1951, when the defection of Guy Burgess and Donald Maclean led to Philby’s enforced resignation from the service he was one day expected to lead, until 1963, when he climbed aboard a Soviet freighter in Beirut, the former golden boy of MI6 was protected by his former employers, seemingly in denial about the titanic scale of his deceit....

Philby’s next appointment, just before the war’s end, was a spectacular success for the KGB: director of the anti-Soviet section. Head of station in Turkey followed and then Washington, where Philby was in charge of liaison between MI6 and the CIA, another crown jewel of a post. His appointment as ''C’’, chief of the Secret Intelligence Service, beckoned. But then it fell apart. US code-breakers had found proof that Maclean, a diplomat, was working for the Russians. Philby sent Guy Burgess, his friend and fellow KGB agent, to warn Maclean. Maclean and Burgess fled to Moscow in May 1951 and Philby found himself the centre of suspicion, the so-called Third Man. Recalled to London, he was subjected to hostile interrogation.

“Kim was in a state almost of shock,” says Milne. “The brilliant career, the high hopes had vanished and he was now an outcast.” MI6 was in shock. Sir Stewart Menzies, chief of the service, had no choice but to ask Philby to resign. “Many people in SIS who, like myself knew very little of the case against Kim, clung to the belief that he was innocent of any serious offence,” Milne recalls.

“The general office belief was that he’d had to go simply to preserve good relations with the Americans. There were very few people in the service who had inspired so much trust and respect as Kim. It seemed impossible that he had done anything worse than act a little unwisely.”

Philby, says Milne, was distressed at having to face interrogation by counterparts in MI5, like Dick White, with whom he had worked.

“It may seem strange that the attitude of SIS and MI5 friends should have mattered so much to him, but I am sure that one part of Kim was fully and genuinely involved in his SIS life,” reflects Milne.

Over the next decade, MI6 continued to argue that there was no evidence against Philby, persuading White, when he became head of MI5 in 1953, to drop the investigation. When in 1955 Harold Macmillan, then foreign secretary, cleared Philby in Parliament, MI6 sent him back into the field, operating in the Middle East as an agent under journalistic cover. “Before long it appeared that the atmosphere had changed,” Milne writes. “Kim was no longer considered a total outcast. I received an elated postcard from him.”

Then, in late 1962, Flora Solomon, a long-time friend of Philby, tipped off MI5 that he had tried to recruit her to the communist cause in 1937. Dick White, now head of MI6, decided to offer Philby immunity in return for the truth. Nicholas Elliott, one of Philby’s supporters in MI6 and a former head of station in Lebanon, went to Beirut to interview him. Elliot botched the interview, allowing Philby to write his own confession and failing to get him to sign it. Elliott believed Philby when he claimed that he had only been a spy up until 1946, which is when arguably his most productive period for the Russians began. The MI6 officer even sought Philby’s advice on seven suspected cases of Soviet penetration. Philby mentioned Milne.

“Kim apparently said that he had mentioned me (among others) to the Russians as someone they might find it worth approaching,” recalls Milne. “However, he went on to say that they had turned the idea down. I was horrified. I think my immediate reaction was to say something like, 'How dare he?’”