In March 1950, Harwell scientist Klaus Fuchs (below) was convicted at the Old Bailey of passing secrets of British atomic and hydrogen bombs to the Soviet Union. His trial took less than an hour-and- a-half, during which time he quietly pleaded guilty to the charges.

Fuchs, the Quaker son of a Lutheran pastor, was born in Russelsheim, Germany in 1911. He attended both Leipzig and Kiel Universities but, as a Communist, was persecuted by the Nazis. He fled through Switzerland and France to Britain, where he attended in succession Bristol and then Edinburgh Universities. In 1940 he was taken into custody as a German ‘enemy alien’ and shipped off to an internment camp in Quebec, Canada.

In 1941, with the help of his old professor at Edinburgh, Max Born (himself a Jewish refugee from Germany) he was back in Britain — and in 1942 he obtained a job with the ‘Tube Alloys’ project (code name for the British atomic research programme).

He was naturalised British in 1942 and, ironically, he signed the Official Secrets Act at about the same time as he started meeting ‘the girl from Banbury’, really Ruth Werner, a German communist working for the Soviets. He was given the code name Rest.

In late 1943, he was transferred to New York to work on the US atomic bomb programmme at Columbia University; then, in the summer of the following year, he started work at the Theoretical Physics Division on the hydrogen bomb at Los Alamos in New Mexico — and it was here that his genius began to shine forth. Together with John von Neumann he filed a patent, far ahead of its time, for initiating fusion and implosion in an H-bomb.

In 1947, he became the first head of the Theoretical Physics Division at the Harwell Atomic Energy Research Establishment, which had been set up at the instigation of Frederick Lindemann, Lord Cherwell (1886-1957), Churchill’s scientific adviser — who was also Oxford University professor of experimental philosophy and the director of the Clarendon Laboratory.

While at Harwell, Fuchs met Soviet agent Alexander Feklisov (1914-2007) at least twice: on September 28, 1947, and on March 13, 1948. On the first occasion, he gave top-secret information about the American super H-bomb and how scientists Fermi and Teller had proved its workability. On the second, he gave away secrets which, according to Russian scientist German Goncharov, “played an exceptional role in the subsequent course of the Soviet thermonuclear programme”.

But, chillingly, historian Lorna Arnold says in her authoritative book Britain and the H-Bomb (Palgrave, 2001), Fuchs was not the only source of information for Russia. She writes: “One Russian source says that at least ten British spies — apart from the American spies — supplied the Soviet Union with nuclear secrets.”

Argument still rages among scientists and academics as to how valuable Fuchs’s reports really were to the Russians with regard to the H-bomb. But his arrest, thanks to the cracking of Soviet ciphers by the joint US/UK project known as Venona, and his subsequent interrogation, led to the arrest of Julius and Ethel Rosenberg who were subsequently executed by the electric chair in Sing Sing Prison, New York, on June 19, 1953.

Fuchs received a sentence of 14 years in prison, the maximum that the Lord Chief Justice, Lord Goddard, could hand down for the crime of breaking the Official Secrets Act and handing over secrets to a ‘friendly’ power. He was stripped of his British nationality and served just over nine years.

Lord Goddard told him: “You have betrayed the hospitality and protection given to you by this country with the grossest treachery.” He was released in June 1953 and emigrated to communist East Germany where he married a friend from his student days and continued his scientific career. He died in Dresden in 1988.