He worked at Bletchley Park during World War II, and was head of "Hut 6", a section responsible for deciphering messages which had been encrypted using the German Enigma machine.

Born in Hendon, London, Philip Stuart was the second of six children to a Professor of German and Teutonic Philology at the University College of North Wales, Edward Leopold Milner-Barry, who died from heart failure in 1917,[1] and his wife, Edith Mary.

[9] Arriving in early 1940, he joined Welchman's "Hut 6" section, whose task was to solve the Enigma cipher machine as used by the German Army and Air Force.

[2] In 1993, Milner-Barry wrote that "to this day I could not claim that I fully understood how the machine worked, let alone what was involved in the problems of breaking and reading the Enigma cipher".

[11] Finding reliable cribs was a critical task for Hut 6, as Enigma was broken primarily with the aid of "bombes", large electromechanical machines which automatically searched for parts of the correct settings.

[14] At this time, Bletchley Park was experiencing a shortage of clerical staff which was delaying the work on Enigma, and the management of GCCS appeared unable to obtain the resources needed.

Together, Welchman, Milner-Barry, Turing and Alexander bypassed the chain of command and wrote a memorandum directly to the Prime Minister, Winston Churchill, outlining their difficulties.

[14] In autumn 1943, Milner-Barry took over as head of Hut 6, which by that time had grown to over 450 staff, Welchman having been appointed the Assistant Director of Mechanisation at Bletchley Park.

[2] His entry in the Oxford Dictionary of National Biography notes that, "although he increasingly felt that Hut 6 was on the verge of losing the ability to decode Enigma, it held on until the end of the war, and this was due in no small part to his gifted leadership.

"[2] The official history of Hut 6, written immediately after the end of World War II, comments on his early "most vital technical achievement" in finding cribs, and on his "administrative and diplomatic talents" in his later role as head of the section.

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.

[6] His obituary in The Independent recalled his "savagely effective attacking style, honed to perfection through a series of 'serious friendly games' against his old rival Hugh Alexander".

[3] In 1992, echoing his wartime visit to 10 Downing Street, Milner-Barry was a member of a party who delivered a petition to the Prime Minister calling on the government to help preserve Bletchley Park, which was then under threat from demolition.