A new book claims to reveal conclusive proof that an Austrian scientist was a spy who worked at the heart of Britain's wartime nuclear bomb programme.
By Leonard Doyle in Washington
Last Updated: 5:50PM BST 09 May 2009
Based on secret KGB documents, it names Engelbert Broda, an Austrian physicist and secret communist sympathiser, as a mole who worked at Britain's Cavendish nuclear laboratory.
Codenamed "Eric" by his Russian handlers, he is believed to have passed thousands of pages of top secret documents about British and American atomic research to Moscow, and was regarded as one of the Soviet Union's most valuable moles. He demanded no payment for his services, and would meet his handlers up to three times a week to pass details of the "tube alloys project", as the nuclear project was officially known.
Eric's true identity has been a matter of speculation for decades. But Spies, the Rise and Fall of the KGB in America, which draws heavily on previously undisclosed Soviet-era intelligence documents, alleges that he was definitely Broda, who fled Austria after Hitler annexed it in 1938.
One of the book's authors is Alexander Vassiliev, a columnist on a Communist Party newspaper, who was given unprecedented access to KGB files for an official history soon after the collapse of the Soviet Union - but who later left for the West with his smuggled notebooks.
His book cites numerous KGB documents, including a telegram from the KGB station in London, informing Moscow about its latest star recruit.
Eric offered his services to the KGB via a contact at Cambridge, and "gave his full consent to work with us," the KGB station chief told Moscow.
Between 1942 and 1945, Eric would travel to London up to three times a week, marking a page in a phonebook in a public callbox whenever he was ready to talk. KGB agents would go to the callbox and pretend to leaf through the phone book before meeting him at an agreed location. So confident were they of not being monitored that they dispensed with such techniques as "dead drops" to transfer secrets.
By August 1943 a Moscow report cited Eric as "the main source of info on work being done on Enormous (the codeword for nuclear bombs), both in England and the USA". Details of the Manhattan Project (America's top secret programme to develop the first nuclear bomb) were in the hands of Soviet spies almost as soon as they arrived at Cavendish.
The success of Russia's wartime atomic spying networks eventually paved the way for Stalin to test Russia's first nuclear bomb in 1949, three years ahead of Britain. Concern at the leaks meanwhile caused America to shut down the flow of nuclear information to its closest ally.
After the war, Broda returned to Austria where he had a distinguished career as a professor of physics and environmentalist. He died in 1983 and has a "grave of honour" at a Vienna cemetery.
Despite strong suspicions that Broda was a communist spy, however, MI5 never found conclusive evidence. Today a history section on its website states that "We feel sure that Broda was engaged in espionage during the war, although we have no proof of it."
But the book's authors believe that detailed contemporaneous notes of Soviet intelligence documents provide the solid proof that MI5 never found. The notes were compiled by Mr Vassiliev, who was invited to inspect KGB files shortly after the Soviet Union's collapse, when the intelligence service felt under pressure to prove that it had scored major coups. Mr Vassiliev then smuggled his notes to the USA in 2001, since when he and fellow researchers have conducted detailed cross-checks which they claim leaves no doubt as to who Eric really was.
Broda is also thought to be the man who recruited British physicist Alan Nunn May to the KGB. A fellow Cambridge scientist, Dr Nunn May received a 10-year jail sentence in 1946 after admitting that he had passed nuclear secrets to Russia. He married Broda's ex-wife Hildegarde after being released in 1952, leading MI5 to suspect some link between the two men, but refused to say who had recruited him even on his deathbed in 2003.
Eric ranked alongside "Liszt" and "Tina" as among the three most valuable Soviet wartime spies in Britain, and until now was the only one whose identity had remained uncertain.
Liszt, unmasked long ago, was the codename for John Cairncross, who worked for the Foreign Office and MI6 while keeping the Soviets informed about Britain's atomic bomb project.
Tina was exposed in 1999 as Melitta Norwood, a former civil servant from Bexleyheath who was by then aged 83.
* Spies, the Rise and Fall of the KGB in America by John Earl Haynes, Harvey Klehr, and Alexander Vassiliev, is published in Britain in July.