Early life, military service, and education
Robson was born in a rural part of Middlesex, that would later become part of the Parliamentary constituency of Finchley and would be known as North Finchley. His father was a buyer and seller of pearls in Hatton Garden, which was sufficient to give a middle-class living. It was a Jewish family and Robson was brought up in that religion, but like many Fabians, he later adopted a perspective of humanist agnosticism.
Robson left school at age 15, without taking examinations, due to his father's death leaving the family in considerable financial difficulties. He got a job as a clerk for the Grahame-White Aviation Company, which operated Hendon Aerodrome; then while still in his teens became the assistant manager of the aerodrome itself.
With the air conflict during World War I underway, Robson joined the Royal Flying Corps in 1915. Part of the RFC's Military Wing, he was a fighter pilot.
In early 1916, while in service, Robson published with Macmillan a book about aviation, Aircraft in War and Peace. In a positive review at the time, Flight magazine described the book as portraying, in non-technical language, the past, present, and possible future roles of aircraft, as well as how aircraft are built and how pilots are trained. A retrospective review characterized it as "a rather good wartime book" that captured some of the sensations flyers felt when they were aloft.
In July 1916, Robson was promoted to Second Lieutenant. He served in both France and in defence of home country during nighttime Zeppelin raids against London. He eventually held the rank of Lieutenant. He left the service, by this time known as the Royal Air Force, in 1919.
Robson's life took a fortuitous turn towards the end of the war. Famed playwright and polemicist George Bernard Shaw, eager to seem modern with the times, wanted to take an aeroplane flight, and (since he had read Aircraft in War and Peace) chose Robson to give him that experience. After landing, Robson admitted to having no plans for after the war, in response to which Shaw said he should go to the London School of Economics (LSE) and wrote him a note of introduction to Sidney Webb, co-founder of the school. Having left school at a young age, Robson lacked the necessary qualifications for entry to LSE, but with the urging of Shaw and upon the recommendation of Webb and his wife Beatrice Webb, another co-founder of the school, he was admitted. As Robson later observed, "however well we plan, there is a lot of accident in career and history."
Robson earned a B.Sc. in Economics with first-class honours from LSE in 1922, followed by a Ph.D. in 1924. He was at the same time reading law, and was called to the bar at Lincoln's Inn in 1922. He then earned an LL.M. in 1928.