Body Parts alludes to Lee's observation that the body has become increasingly important to biography over the past century. Illness, menstruation, masturbation and addictions are seen as permissible, even crucial, fodder for the biographer.

'The division that tended to be made in earlier biography between the life of the body and the life of the mind has been eroded,' Lee says.

She is suspicious of biographies which reduce people to their ailments. 'My anxiety comes when a figure like Virginia Woolf is treated always as a victim - a victim of mental illness, a victim probably of childhood sexual abuse, a victim of her bodily functions.'

Cautioning biographers against trying to own their subjects, Lee insists that a biography is merely one view of a life that can never be pinned down. 'While you're doing the work, you have to feel, 'I know more about this person than anyone living'. But the minute you've done the work, you have to let it go. These wonderful writers don't belong to you, they belong to the world.'

Since Lee published Willa Cather: A Life Saved Up in 1989, various groups have laid claim to the early 20th-century novelist from Nebraska. Some theorists sought to recruit Cather as a lesbian icon, provoking a backlash from traditionalists who resisted attempts to politicise her.

Lee says she would approach the book differently today. 'I was very interested in the treatment of women in the books but ... I perhaps didn't think hard enough about the relationship between that and her own sexuality.'

For all her reluctance to be possessive of her subjects, Lee flinched at the portrayal of Woolf in Stephen Daldry's film, The Hours. Woolf wrote Mrs Dalloway in her early 40s and committed suicide at age 59, but Lee argues that the film makes it seem that she killed herself immediately after completing the novel.

Lee was also troubled by Daldry's romantic recreation of Woolf's suicide, in which she 'drifts into this beautiful green leaf-shaded river with birds singing and wonderful throbbing music and sun playing on the dappled water'.

Actually, Lee says, 'Woolf killed herself in great agony of mind, on a bleak day in March, in a river where the water runs so fast that nothing grows on the banks.' When Lee confronted Daldry about his travesty of Woolf's death, he retorted that Nicole Kidman could only film in July.

In Virginia Woolf (1996), Lee was careful to keep the author's suicide mysterious, wary of the tendency of biographers to use deathbed scenes and last words to sum up a life. 'I'm very interested in our desire - even now, in a secular, generally sceptical era - to invest a death with some significance and not just see it as an arbitrary happening.'

At age nine, Lee read the opening pages of Woolf's The Waves. It doesn't surprise her that she responded to Woolf so young, since she sees her novels as presenting a child-like worldview - a quality that explains why her undergraduate students generally prefer Woolf to, say, Edith Wharton. 'I think you've got to be older and have had some bitter personal experiences before you get on with Edith Wharton.'

Lee's 853-page biography of Wharton, the first woman to win the Pulitzer Prize with The Age of Innocence in 1921, was published last year to huge acclaim. The relationship between Wharton's life and work interested Lee because 'she is not a confessionally autobiographical writer. This is someone who doesn't say 'I' except in her poems. She disguises and objectifies her material.'

Lee attributes the painstaking detail of the book to Wharton's influence. 'What she does is to give a very vivid sense of history through fiction, so I wanted to go in for that kind of thick description.' Lee sought to rescue Wharton from her reputation as 'a sort of inferior Henry James' that she developed after falling out of fashion in the 1930s, when she came to be seen as posh.

She structured Edith Wharton thematically rather than chronologically; the chapters resemble interconnected chambers, mirroring Wharton's interest in interior design. 'I wanted the structure of it to be rather like going into a series of rooms, so that you would have the Henry James room, or the Italian room, or the terrible room of France at war,' Lee says.

Such a detailed biography is out of step with publishing trends, she suggests. 'It may be that these sorts of biographies are not going to be much written any more. People are increasingly interested in writing collective biographies, or short biographies of parts of a life, or biographies of much less well-known figures.'

Lee is 'having a little rest' after the eight-year labour of Edith Wharton before committing to another biography. Meanwhile she's writing a pocket-size book on the history of biography for Oxford's Very Short Introductions series.

It's only since the 1980s that biography has become a part of academic study, Lee says. 'It has to do with the history of modernism - figures like T. S. Eliot, saying, 'The work has nothing to do with the life'. Now people are much more interested in mixed genres, mixed approaches.' Lee started a course on life-writing at Oxford, where she lives with her husband, Keats scholar John Barnard.

Thomas Carlyle said the primary requirement for a biographer was to have 'an open loving heart'. But while Lee is motivated to write literary biography by enthusiasm for the writer's work, she doesn't think it's necessary to like them as people. 'This is a job of work, not a love affair. I'm a little sceptical about empathy as the driving force of biography.'

More comfortable as biographer than subject, Lee responds archly to personal questions. The younger of two daughters, she grew up immersed in culture. Her father, a retired family physician, was a cellist; her late mother, who left school at 15, was a self-educated but ravenous reader. A bookish childhood led to an English degree at Oxford, where Lee stayed for her doctorate.

Last year, a friend described her to the press as General Lee. Is her reputation for bossiness fair? 'No, I'm fantastically sympathetic and gentle,' she says, deadpan, before adding. 'I think I'm perhaps a bit, um, driven.' It's difficult to know which image is true. Probably both are. Two of the several - or thousand - selves of Hermione Lee.