The 1956 Olympiad trip to Moscow was risky, since Britain and the USSR, which had been allies during World War II, were by then locked into the Cold War, and Milner-Barry's wartime codebreaking knowledge would have been of great interest to the Soviets; the very fact that Britain had broken German codes on a massive scale was kept secret until 1974, when Frederick Winterbotham's book The Ultra Secret was published.
The 1956 Olympics trip to Moscow posed a significant risk due to the escalating Cold War tensions between Britain and the USSR, who had been allies during World War II. Milner-Barry's wartime codebreaking expertise would have been highly sought after by the Soviets, given Britain's successful history of breaking German codes. This secret remained hidden until 1974 when Frederick Winterbotham's book "The Ultra Secret" was published.