He placed fifth in the first International Correspondence Chess Federation (ICCF) World Championship tournament (1950–1953), and inflicted the only defeat on the eventual champion, Australian Cecil Purdy.
In the mid-1930s, he joined the research department of Conservative Central Office, led by Sir George Joseph Ball; Mitchell served as a statistician.
His subsection's role was to maintain surveillance on suspected Nazi sympathizers and right-wing nationalist organisations such as the British Union of Fascists as well as German and Austrian political bodies.
Mitchell assisted Francis Aiken-Sneath in investigating Sir Oswald Mosley's activities and in organising the case for his wartime detention.
[8] In May 1951 diplomats Guy Burgess and Donald Maclean had defected to Moscow, and Mitchell led the MI5 team investigating what Soviet penetration there might have been in Britain's intelligence services.
[10] Chapman Pincher, an investigative journalist specialising in the intelligence services, wrote of the paper "it was strewn with statements now proven to be false – as they were known to be inside MI5 at the time".
While not defending or agreeing with his father or supporting his detention, Francis Beckett said of Mitchell "the satisfaction in the covert control he exerted over other people shines through his flat prose", and that the memoranda show signs of reluctance to later give up the arbitrary power over the freedom of others that had been granted in 1940.
[1] A few years later, it seemed highly likely that Kim Philby, in the SIS at the time of the Burgess–Maclean defections, had been tipped off that he was about to be confronted with conclusive evidence of his treachery, and this led to his decampment from Beirut to Moscow in 1963.
[1][16] The main suspicion then fell on Hollis and, although the matter has never been completely resolved, Christopher Andrew in his Authorized History of MI5 comes to a firm conclusion that neither were traitors.
[17] Andrew states that Harold Wilson wrote on Trend's review of the Hollis and Mitchell cases: "This is very disturbing stuff, even if concluding in 'not proven' verdicts".
[19] On the day of publication of Pincher's book, Prime Minister Margaret Thatcher made a statement in the House of Commons disclaiming Pincher, not mentioning Mitchell, but saying of Hollis that while the investigation "did not conclusively prove his innocence" that "Lord Trend, with whom I have discussed the matter, agreed with those who, although it was impossible to prove the negative, concluded that Sir Roger Hollis had not been an agent of the Russian intelligence service".
[21] The accuracy of various allegations made in the book by Wright was questioned in a review of Spycatcher published by the Center for the Study of Intelligence, an in-house think tank for the CIA.
While admitting (on page 42) that the book included "factual data", the document stated that it was also "filled with [unspecified] errors, exaggerations, bogus ideas, and self-inflation".
But somebody was doing it" [23] The 2014 MI5 website addresses the matter specifically, stating that the original investigation lasted from 1964 to 1971 but "came to no firm conclusions" and that Trend's report concluded "there was no evidence to show that either Hollis or Mitchell had been Soviet agents".