It was Private Eye's anonymous critic, reviewing a Yann Martel novel, who warned of the dangers of writing about animals and allegory. He (or she) could usefully have gone on to advertise some of the perils of writing a biography of a living person. First, there is the problem of getting the subject on your side and keeping him there, never mind the threat to your objectivity that this relationship may nurture. Then there is the task of cajoling people who know him (who may regard the enterprise as a vanity project) to talk. Finally, there is the thought that most of your conclusions will necessarily be provisional, as the person may have two or three decades of vigorous existence still to live.