 After a fellowship at Harvard University, he began his career as a civil servant in the Treasury, before being elected to a fellowship at Trinity College, Cambridge in 1946.From 1961 to 1976 he was Professor of English Law at Oxford University and a fellow of St John's College, Oxford, and from 1978 to 1982 Rouse Ball Professor of English Law at Cambridge University; from 1976 to 1988 he was Master of Gonville and Caius College, Cambridge.He held the degrees of MA and LLD, and the honorary degree of LittD from Cambridge University.