John Cook was the only child of a quiet father who was a talented painter and who never wholly recovered from the effect of gas in 1917. A somewhat isolated childhood led to the development of a considerable intellect. After the Wyggeston School in Leicester he was a Squire scholar of Downing College, Cambridge. This was followed by a Tancred Studentship at Lincoln's Inn and a short time spent as a pupil on the Midland circuit. He overcame his regret that he had been unable to practice at the Bar.