Alister McGrath’s fine new biography of C.S Lewis comes garlanded with an unnecessary and potentially misleading subtitle: “Eccentric Genius, Reluctant Prophet”.

Genius and prophet he clearly was, as Dr McGrath demonstrates. He was reluctant, too, in the latter role — understandably, for his being in the limelight attracted both opprobrium for what were, in Oxford, his unfashionable Christian views and prurient interest in his somewhat unusual domestic arrangements which involved sharing his house (and bed?) with a woman, Jane Moore, old enough to be his mother.

But eccentric? In the academic world through which Lewis moved during his English teaching days — first at Oxford’s Magdalen College, then at its namesake (plus an ‘e’) beside the Cam — the adjective calls to mind a wild-eyed, wild-haired figure in the mould of Professor Branestawm.

A far cry, this, from the sober-suited, pipe-sucking gent who might have been observed downing pints with his fellow Inklings in the back bar of the ‘Bird and Baby’, in St Giles, as they discussed their books-in-the-making, the Narnia stories in Lewis’s case, Lord of the Rings in Tolkien’s. The quantity of beer might surprise readers of more ascetic tastes (as might Lewis’s appetite for sado-masochism, revealed ‘in drink’ during his Oxford student days). His consumption was as nothing, though, compared with that of his alcoholic brother and housemate, Warnie, when on a bender. One was triggered by Lewis’s death on November 22, 1963. In bed guzzling whisky at the Kilns, in Headington Quarry, Warnie missed the funeral four days later.

The ‘Lewis industry’ of recent years (well analysed here) has ensured that the facts of his life are well-known. As a former Oxford professor of historical theology, Dr McGrath is able to add to the story much compelling detail on how and why Lewis is a source of religious inspiration to millions, especially in the US.