'No one can write a man's life but those who have ate and drunk and lived in social intercourse with him': Samuel Johnson's saying, however questionable (what about his own Lives of the Poets, for a start?) contains an important truth. Biography is a treacherous genre because it assumes an authoritative knowledge of its subject's motives and actions - a knowledge which in reality no sane person can claim to have about another, however intimately acquainted or fully documented. Contemporary biographies notoriously tend towards revelation; yet the more probing they are, the more they reveal about the biographer. No one can write about another person's personality and actions without judging them, and in the quality of those judgements (both editorial and moral), the writer's own personality is revealed, sometimes all too plainly. To write another person's life doesn't only demand scholarship and narrative skill; it also calls for what Jane Austen called in another context 'the less common acquirements of self-knowledge, generosity and humility', for one cannot begin to judge another person's motives and actions intelligently (especially when these are unorthodox) without being prepared, however privately, to scrutinise one's own. Thekla Clark's is the first account of Auden to stand up to this alarming ethical challenge without falling prey to the Scylla of self-righteous prurience or the Charybdis of uncritical identification.

In other words, this book bears Johnson out: the writer, a close friend of Wystan Auden and his partner Chester Kallmann for more than twenty years, ...