JOHN Cairncross, the Fifth Man in the Cambridge spy ring, gave the Russians the atomic bomb, according to KGB documents.Cairncross always claimed that he only passed the Russians secrets when they were Britain's allies against Hitler. He insisted that he never gave them atomic secrets and denounced suggestions that he was the Fifth Man as an elaborate conspiracy by MI5, the British security service, and the KGB.
But the files, released to the Daily Telegraph, show this to be nonsense and his claims never to have damaged British interests to be a lie.
Cairncross not only passed the Russians secrets before the German invasion of the Soviet Union in June 1941, when Stalin was Hitler's ally. He gave them even more during the Cold War.
But the pinnacle of his KGB career was when he was secretary to Lord Hankey, Minister without Portfolio in Churchill's war cabinet.
During this time, Cairncross handed the Russians details of the British atomic weapons programme, giving Stalin the information he needed to build a bomb.
The KGB files on his treachery were released for The Crown Jewels, a new book by the spywriter Nigel West, pen name of Rupert Allason, the former Tory MP, and Oleg Tsarev, a former KGB officer.
Cairncross denied being the Fifth Man, describing himself grandly as `The Enigma Spy' in an autobiography published last year two years after his death. The title referred to files passed to the KGB when he worked at Bletchley Park, home of Britain's wartime codebreakers. Cairncross gave the Russians intercepts of German plans for the Battle of Kursk, a move that is believed to have helped to turn the tide against the Germans on the Eastern Front.
The Cambridge Spy Ring began to unravel in January 1949, when American intelligence officers deciphering messages between Moscow Centre and its overseas stations discovered evidence of a previously unknown Soviet agent.
Codenamed Homer, the Russian spy had been based in Washington in mid-1945 and had access to the secret conversations between President Truman and Winston Churchill.
In April 1951, the codebreakers made the crucial breakthrough. A KGB message dated June, 1944 said Homer's wife was pregnant and staying with her mother in New York.
The FBI and MI5, the Britain's domestic intelligence service, had already narrowed down the people with access to the Truman-Churchill messages to around five. Of these, only one had a pregnant wife in June 1944: Donald Maclean's American wife Melinda had spent her confinement with her mother in New York.
Kim Philby, an officer with MI6, the foreign intelligence service, who was a key member of the Cambridge spy ring, was in Washington and was briefed on the discovery. He sent Guy Burgess, another member of the ring, to England to warn Maclean.
On May 25, 1951, Maclean and Burgess drove to Southampton and boarded a ship bound for St Malo. In France, they were given false documents by the KGB and made their way to Moscow. The defection of Burgess immediately linked Philby to the affair.
Although Cairncross conceded that he was recruited when Hitler and Stalin were allies, he provided nothing of significance at that time.
It was, he said, a ``closed season'' in his relationship with the KGB, while during the Cold War the links were ``merely formal'' and what information he passed to Moscow was ``relatively innocuous''.
But the files make it clear that Cairncross was not only lying over the extent of his treachery, he was also lying over his motives.
(Daily Telegraph, London)