[2] As a scholarship student at Trinity Hall, Cambridge, he achieved a first in physics, which led to doctoral studies under Charles Ellis and lectureship at King's College London.

During World War II, May initially worked on radar in Suffolk and then with Cecil Powell in Bristol on a project that attempted to use photographic methods to detect fast particles from radioactive decay.

The team was part of the British Tube Alloys directorate that was merged into the American Manhattan Project, the successful effort to create a nuclear weapon.

He had let his membership of the Communist Party lapse by 1940, but at Cambridge, when he saw an American report mentioning that Germany might be able to build a dirty bomb, he passed that on to a Soviet contact.

The courier of the samples was not informed of the danger of radiation, developed painful lesions and needed regular blood transfusions for the rest of his life.

May refused to define his actions as treason and claimed in a statement after his release from prison that he believed that he had "acted rightly" as a spy because of being "wholeheartedly concerned with securing victory over Nazi Germany and Japan, and the furtherance of the development of the peaceful uses of atomic energy.

May is a major character in the 2003 novel The Cloud Chamber, by Clare George, a fictional account of Cambridge physicists in the 1930s which centres on the scientific excitement of the interwar years contrasted with the vexing moral questions faced by scientists during World War II.