So, he might have been a little chary of McGrath's book, the work of an evangelical Anglican, and an important one. But no:
There have been plenty of biographies of Lewis—I once wrote one myself—but I do not think there has been a better one than Alister McGrath’s. He is a punctilious and enthusiastic reader of all Lewis’s work—the children’s stories, the science fiction, the Christian apologetics, and the excellent literary criticism and literary history. He is from Northern Ireland, as Lewis was himself, and he is especially astute about drawing out the essentially Northern Irish qualities of this very odd man. And he is sympathetic to the real oddness of his story.. . .McGrath's book is as good as Wilson says--although a less compelling read than Wilson's own, greatly helped by Wilson's novelist's skill as a storyteller. It's a first rate biography of a figure whose complexity and depth not merely of thought, but of feeling, do not always, as I have previously argued, receive the respect he deserves, nor does the breadth of his view of orthodoxy.
Where McGrath is so good is in sorting out the truth of this story. Lewis remembered, shortly after his conversation with Tolkien, being driven in the sidecar of his brother’s motorbike to an outdoor zoo—Whipsnade. In the course of this journey, he decided he believed in the Incarnation of Christ. He remembered his exultation as the two brothers walked together among bluebells. But, McGrath, points out, it was September—when bluebells are not in flower! McGrath cunningly shows us that the moment of epiphany must in fact have come two years later, when Lewis went to the zoo with his lover, or former lover Mrs. Moore and her daughter Maureen.
Mrs. Moore is the most understandable omission from Lewis’s autobiography. (Another being Lewis’s obsession with sadism; he nicknamed himself Philomastix, or Lover of the Whip). McGrath deals with the whole story remarkably fairly. Lewis trained as an officer to fight in the First World War, and shared a room with a man called Paddy Moore. The two boys agreed that if either were killed in the war, the other would look after the dead one’s parent. Moore was killed. Lewis had already begun a relationship with Janey Moore, with whom he subsequently lived for the rest of his life. When I wrote my life of Lewis, I speculated, as others have done, that they must have been lovers—though this was always hotly contested in those days by some of Lewis’s more pious admirers. When my book was published, Maureen, Mrs. Moore’s daughter, smilingly told me she was glad I had realized what she had been trying to tell me during our conversations about her mother.
Until reading McGrath, I had never before been so struck by the fact that Lewis was a poet manqué. Of course I had known this—it is the most obvious fact about Lewis the writer. His earliest printed works were poems, but they were no good. He never quite recognized this fact, and the people he truly hated tended to be poets. One of his first pupils at Magdalen was dear old John Betjeman, later poet laureate, but Lewis the sadist treated him abominably. Lewis loathed T.S. Eliot and could not see any virtue in Eliot’s work, even after he became a Christian. Lewis once had a fight in a pub with the poet Roy Campbell. To this degree, he was the classic case (we have all met them in university life) of the secondary talent who could not endure primary talents. Brilliant as an exponent of the virtues in Spenser, Dante, Chaucer, Lewis could not write his own poetry.
Yet toward Tolkien he remained wonderfully generous. Without Lewis’s prompting, there would have been no Lord of the Rings. The only new bit in McGrath’s book that made me cry was a letter he has unearthed in which Lewis proposed Tolkien for the Nobel Prize for Literature. By then the friends were more or less estranged. Tolkien disliked Lewis’s Narnia books intensely and he resented his friend’s marriage to Mrs. Davidson. Yet Lewis never returned Tolkien’s rancor. The cooling of friendship is as sad as the death of other kinds of love, and McGrath conveys this beautifully. His book evokes with aching honesty that vanished male world of heavy-smoking, heavy-drinking Oxford, the world in which emotions are not investigated, not understood, and left at home with the usually unhappy womenfolk
I can say that Alister McGrath, like A.N. Wilson before him, does justice to Lewis. Indeed, he does finer and better justice than Wilson could; as Wilson acknowledges, McGrath's use of previously unavailable original sources, his precision in reckoning the chronology, corrects Wilson's own book, and illuminates places in Lewis's landscape that Wilson missed. I admire Wilson's magnanimity in admitting this, and McGrath's achievement. It is no small thing to write a good biography of a figure like Lewis; to write a great one, as I believe McGrath has, is extraordinary.
Here's an introduction to McGrath's biography, by the man himself: