One of Harold Macmillan’s biographers described the politician’s lifelong Anglican faith as the bedrock of his character. Yet as a young man, under the influence of the beguiling Ronald Knox, he had teetered on the brink of conversion to Rome

In 1912, an 18-year-old Harold Macmillan, beginning his studies at Balliol College, Oxford, discovered, to his surprise, that his next-door neighbour was a priest. To his even greater surprise, it was a priest he knew: Ronald Knox. Knox’s star-studded future as a Catholic apologist was all in the future. For now, he was the Anglican chaplain of Trinity College. In a startling coincidence, he also happened to be Macmillan’s old tutor. When the future Prime Minister had left Eton in 1910 for health ­reasons, his mother, the formidable Helen (known as Nellie), employed Knox as a classics tutor, replacing his brother Dillwyn Knox, who had left when he was judged to be ­“austere and uncongenial”.

Macmillan and Knox struck up a close ­rapport. The new tutor discussed religion with his pupil, even taking him, at the boy’s request, to High Mass. Knox didn’t swim the Tiber until 1917, but his journey to Rome had begun nearly a decade before. The son of an evangelical Bishop of Manchester, Knox made little effort to hide his sympathies; after his ordination as an Anglican priest in 1912, the young vicar dressed in Roman fashion and celebrated Mass in Latin.