Andrew Cook compares notes from Soviet sources and recently released MI5 files on Klaus Fuchs, the British nuclear physicist and spy who helped the Soviet Union develop the atom bomb.
As Head of the Russian Secret Police, the NKVD, Lavrenti Beria was, after Stalin, the most feared man in the Soviet Union. At the best of times a suspicious man, Beria was particularly sceptical about a host of reports that had landed on his desk during the course of 1941, indicating that the British and Americans were working on atomic research. In his view it was more than likely a ploy to lead the Soviet Union into a costly and ultimately unproductive scientific cul de sac.
However, through material provided by Cambridge spy John Cairncross and later by a source actually working on the British bomb project, he began losing some of his doubts. Nevertheless, it is clear that even after the decision had been taken in 1942 to explore the feasibility of developing a Russian atomic bomb, Beria was still sufficiently sceptical to tell Soviet scientists working on the project that, ‘if this turns out to be deception material, down you all go into the cellars!’