It is the 29 May 1951. Two senior figures in the British diplomatic services – Guy Burgess and Donald Maclean – have disappeared, and are beating a secret retreat, we now know, to Moscow, wanted by their British spymasters. Soon it will be all over the newspapers and the greatest scandal in the history of espionage.
But the story, as told from inside MI5 by its affable deputy director Guy Liddell makes for ironic reading. His diaries of the immediate post-war period, which have been disclosed this morning by the national archives, show not only that he didn't have much of a clue what was going on, but what scant detail he did have he shared with the other members of the now notorious "Cambridge Four", Kim Philby and Anthony Blunt.
"The Watchers [surveillance operatives] failed to pick up Maclean since his departure for the country on Friday," records Liddell in his diary.
He then receives a phone call from an individual concerning Burgess's mysterious disappearance.
"He had telephoned either on Thursday or Friday to the wife of Garonway Rees [a friend], when he said he was not likely to see her for a long time. Burgess had remarked that he was going away for the weekend in order to assist a friend who was in some sex trouble and being blackmailed," he states rather simply, before deciding it is "likely to be untrue".
"In view of past association between Burgess and Maclean observed by Watchers, it seems pretty clear that the pair of them have gone off."
The two men were both homosexuals and had been students together at Cambridge. Instructions are sent to all border points to detain the men, but the pair remained hidden for five years, emerging in Moscow in 1956.
With questions being asked of Liddell by everyone from the Prime Minister to the King, Liddell's conclusions now look rather unfortunate.
"It seemed to me unlikely a man of Burgess's intelligence could imagine he had any future in Russia," he wrote. "I find it difficult to imagine Burgess as a Comintern agent or an espionage agent. I feel certain Anthony [Blunt] was never a conscious collaborator with Burgess in any activities."
It was the disappearance of the two men that would unmask Kim Philby, the most senior spy in the group. Were it not for Burgess, Philby remarked years later, he might have made it to the top job at MI6. Two months later Philby resigned from his position at MI5, and was interrogated later by Helenus "Buster" Milmo, a QC.
Milmo, wrote Liddell, was "firmly of the opinion that he is or has been a Russian agent, and that he was responsible for the leakage about Maclean and Burgess", Liddell recorded.
"Personally I feel less convinced about this last point. Philby's attitude throughout was quite extraordinary. He never made any violent protestation of innocence, nor did he make any attempt to prove his case."
In 1952 Liddell was told information suggested Blunt was a more active Communist than originally known, but in July he wrote: "While I believe that Blunt dabbled in Communism, I still think it unlikely that he ever became a member".
MI5 diaries: highlights
The diaries record interest by military officials in the idea that pigeons might be flown by radio control. The head of the Army's pigeon loft, Captain James Caiger, told him how pigeons' homing instinct was affected by sunspots. "This gives some colour to the suggestion that pigeons might be able to home on an electric beam – in other words that you might have radio-controlled pigeons."
On meeting Flight Lt Charles Cholmondeley, who dreamt up the successful Second World War Operation Mincemeat, in which a body was deliberately washed up in Italy containing false information about a planned invasion, Liddell records: "His handlebar moustache is not quite so long as it was. Since he left us he has been pursuing locusts in the middle east and Kenya."
Liddell expressed concern to Winston Churchill when he became Prime Minister again in 1951, on his keeping of a Swiss valet. "Any alien" in his service must be a target, he told him. He asked me whether I meant a target for the enemy or for the press. I said I had been thinking of the enemy, but that of course he would be a target for both."
Liddell sends an officer to Risley in Derbyshire, home of the UK's fledgling nuclear programme, to investigate the curious case of the "luminous" or "radioactive man". The agent noted: "The question arises whether the man has been drinking plutonium water."
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies