John Cairncross was labelled the 'Fifth Man' by the media in a reference to the known 'Cambridge Four'. Cairncross was accused of being a spy for the USSR along with Anthony Blunt, Guy Burgess, Donald McLean and Kim Philby. During the Cold War both sides used spies with a degree of frequency and it was said that Cairncross agreed to spy for the USSR while he was at Trinity College, Cambridge. Anthony Blunt was the person who turned Cairncross who later said that Blunt “was the moving spirit and the main strategist in the KGB's recruiting network at Cambridge”.
Cairncross was born in Scotland July 1913. After attending Trinity College where he studied Modern Languages, he joined the Foreign Office in 1936. During World War Two he worked at Bletchley Park, where Britain's top code experts were stationed. Towards the end of the war, Cairncross worked at the headquarters of MI 6.
Cairncross consistently denied that he was a 'proper' spy - a stand he took until his death. He was also never prosecuted for betraying his country. However, Cairncross did admit to passing to the Soviet Union information during World War Two. He did not consider this to be an issue as he argued that during the war, both Great Britain and the USSR were allies fighting against a common foe. Therefore, he argued, he was merely helping the USSR and by helping them he was, in effect, helping the UK as the sooner Nazi Germany was defeated the better for the UK. For example, Cairncross supplied the USSR with information from ULTRA at Bletchley Park regarding what the Allies knew about German intentions at what was to become the Battle of Kursk. However, he also provided the Soviets with Allied cipher codes, which allowed the KGB to stay one step ahead of the West in terms of code development.
In 1951 Cairncross did admit that he had passed on incriminating information but that it was not his fault, as he had not fully understood the situation he was in. Cairncross admitted that he had passed information on to Guy Burgess but that he never knew that Burgess was a spy.
However, there were those who did not believe him and they believed that Cairncross was responsible for passing to the USSR secrets that related to the development of the atomic bomb and that the information he gave to the USSR acted to kick-start the Soviet atomic programme - such was its value. Old Soviet files show that between 1941 and 1945, Cairncross passed to the USSR nearly 6,000 documents.
In 1990 the Soviet defector Oleg Gordievsky claimed that Cairncross was the 'Fifth Man'.
Not charged with any offence, Cairncross worked as a translator for the United Nations Food and Agriculture Organisation in Rome. When he retired he went to live in South France.
He died in 1995.