The pram in the hall was one spy’s best friend

‘If you had visited the quaint English village of Great Rollright in 1945, you might have spotted a thin, dark-haired and unusually elegant woman… climbing on to her bicycle,’ Ben Macintyre opens his latest book, like the start of a gentle Ealing comedy. It will come as no surprise to his fans that the elegant Mrs Burton, Cotswolds housewife, baker of excellent cakes, mother of three and wife of a chap called Len who works in the local aluminium factory, is in fact Colonel Ursula Kuczynski of the Red Army, aka Agent Sonya, whose clandestine mission is to help the Soviets build the atomic bomb.

Agent Sonya was allocated her code-name by Moscow in 1931, but her formative moment had come seven years earlier, when a brutal police attack during Berlin’s May Day parade transformed her from teenage protestor into lifelong revolutionary. The daughter of left-leaning German Jewish intellectuals, Ursula was articulate, adventurous and ambitious.