Sixth man: Brilliant MI6 scientist Wilfrid Mann

For more than 50 years, the identities of members of the infamous Cambridge Spy Ring have been the stuff of debate and fevered speculation. Four – Donald Maclean, Kim Philby, Guy Burgess, and Anthony Blunt – have been unmasked as Soviet agents.

A fifth is believed to have been the Bletchley Park and MI6 officer John Cairncross. Now author Andrew Lownie has unmasked a sixth Soviet spy at the heart of the Establishment – a brilliant MI6 physicist who sent nuclear secrets to the KGB which allowed the Russians to develop their own atom bomb…

To his colleagues in MI6, scientist Wilfrid Mann was known as ‘Atomic Man’, the conduit between Britain’s nascent nuclear programme and the team of specialists working under Robert Oppenheimer on America’s Manhattan Project in the desert of New Mexico.

But he also had a secret life as a Russian spy, working in the office next door to his fellow KGB agents Donald Maclean, Guy Burgess and Kim Philby in the British Embassy in Washington from 1943 to 1951.

Mann’s role was to use his specialist knowledge to help Maclean interpret information on the latest nuclear developments for the Soviets. Recruited as a student in 1930, he was given the KGB codename Malone, and was regarded in Moscow as an agent of great influence – equal to Philby in importance.

And no wonder. Despite the enormous secrecy surrounding the research, it was barely any time before the Russians – greatly helped by Mann and others – obtained the Anglo-American blueprints for nuclear weapons, and in 1948, to the fury of the West, were able to test their own.

Mann’s treachery has been known for some time in intelligence circles and it is perhaps significant that in spite of his wartime scientific contributions in both the UK and the US he received no obituaries.

Traitors: Donald Maclean, left, and Guy Burgess, right, have already been unmasked as Soviet agents

But he has never previously been named publicly until I uncovered independent documentary proof while researching my new biography of Burgess.

Mann features as ‘Basil’ in journalist Andrew Boyle’s 1979 book The Climate Of Treason, which led to the exposure of Anthony Blunt.

Citing a confidential CIA source, Boyle claimed the Israelis passed on ‘Basil’s’ name to CIA counter-intelligence chief James Angleton shortly after the Second World War as ‘the price for uninterrupted but informal co-operation with US intelligence’.

According to Boyle, American codebreakers revealed separately in late 1948 that a Russian source inside the British Embassy had passed classified information during the final stages of the war.

Boyle wrote that ‘Basil’ was identified and ‘broke down quickly and easily’. He was given the choice of continuing to work for the Russians as a double agent under CIA direction, or face prosecution under American law. He agreed to provide Maclean with useless information in return for immunity from prosecution and American citizenship.

Third man: Kim Philby

Though Boyle did not name Mann, he was easily identified by insiders – his middle name was Basil – and questions were asked in the House of Commons. Indeed, Mann himself denied the allegations in his 1982 book Was There A Fifth Man?

However, Mann does write of his friendship with all three Cambridge spies and gives a particularly vivid account of the famous 1951 dinner party at Philby’s house where Burgess managed to insult the guests – all top US intelligence officials.

I uncovered independent British confirmation of Mann’s espionage activities in the private papers of Sir Patrick Reilly, chairman of the Joint Intelligence Committee and Foreign Office Under-Secretary in charge of intelligence at the time of Burgess’s defection in 1951. Reilly wrote in his unpublished memoirs: ‘That “Basil”, who can easily be identified, was in fact a Soviet spy is true: and also that he was turned round without difficulty.’

Mann was born in London in 1908 and educated at St Paul’s school before going on to receive a degree in maths and physics from Imperial College in 1929 and a physics doctorate in 1934. In 1941, he invented the Jitterbug, the prototype uranium separation machine.

At Imperial he had come under the influence of G. P. Thompson, the physicist in charge of the UK’s nuclear programme, later incorporated into the joint British and American Manhattan Project. After a short period with the British nuclear programme in Canada, he returned to Washington as a member of MI6 as the British scientific intelligence liaison officer – but was suddenly replaced in April 1951, within days of Maclean’s treachery being uncovered.

Mann, who became an American citizen in 1959, declined all interview requests and died in a Baptist retirement home in Baltimore in March 2001.

Fourth man Anthony Blunt, left. The fifth is believed to have been Bletchley Park officer John Cairncross, right,