Martin Rivers Pollock was born in Liverpool on 10 December 1914. He came from an old legal family, being the great-great-grandson of Sir Jonathan Frederick Pollock, Bt. (1783–1870), a Fellow of Trinity College, Cambridge, barrister, MP for Huntingdon, Attorney General in Peel's first administration and Chief Baron of the Exchequer from 1844 to 1866. His father, Hamilton Rivers Pollock, also went to Trinity College, qualified as a barrister but never practised, and in 1914 was with the Cunard Steam Ship Company, before spending World War I with the Liverpool Regiment and the Royal Air Force. His mother was Eveline Morton Bell, daughter of Thomas Bell, of Newcastle-upon-Tyne. After the war his father inherited a fortune from an uncle, and the family moved to Wessex, where they lived first at splendid Anderson Manor, Dorset, and then Urchfont Manor, Wiltshire, his father living as a country squire and JP.
Pollock had a conventional upper-class education, beginning with a nanny, followed by West Downs School (1923–28) and then Winchester College (1928–33). His first scientific enthusiasm was for astronomy, but he decided he was insufficiently mathematical to pursue it further (his mathematics master was Clement Durrell, author of some famous texts including Advanced algebra), so he then decided to study medicine. His Wessex schooldays were influenced by the nearby Powys brothers, the youngest (Llewelyn1) having been a Cambridge friend and contemporary of his father. Through Sylvia Townsend Warner2 he met her cousin Janet, daughter of Arthur Llewelyn Machen3, who eventually, in 1979, became his second wife.
He went up to Trinity College, Cambridge, in 1933, having done his first MB and the first part of his second MB while still at school, and opting to do the two new half-subjects (Pathology and Biochemistry) that had just been instituted—he remembered thinking at the time that biochemistry was going to be the key subject for medicine in the future. Already while at school he had become a theoretical Communist, and as an undergraduate worked very hard, both at his medical studies and in political activity (such as selling the Daily Worker) for the Party—and knew most of the soon-to-be notorious Cambridge Communists of the time, including Guy Burgess4 and Donald Maclean5. He was now a Senior Scholar, and graduated BA first class in 1936; he started to spend a fourth year reading Part II Biochemistry. He decided in April 1937 that he had spent too long at Cambridge, so moved on to his clinical studies at University College Hospital. He also felt he should try to become qualified before what he saw as the inevitable war started, although he was nearly distracted into joining the International Brigade and going off to Spain—he had been a friend of John Cornford6, who did go to Spain and wrote and died there, and of Norman John (but widely known as James) Klugmann.