Hilary Spurling and Kathryn Hughes bring their passion to writing biography. Alicia Clegg hears how they pursue their subjects.

'My mother has a cottage in Wales and for pretty much two years I was there, alone. I had conjugal visits every time I finished a chapter. By the end, I was frantic. I was very surprised not to have had some sort of a breakdown', recalls Hilary Spurling (Somerville 1959).

We have just finished our interview for Oxford Today. Spurling has been telling me about her race to meet the publishing deadline for Matisse the Master, the second volume of her biography of the artist Henri Matisse, for which she won the 2005 Whitbread Book of the Year Award.

With us are the playwright and novelist John Spurling, he of the conjugal visits, and also Kathryn Hughes (LMH 1978), author of The Short Life & Long Times of Mrs Beeton, who has arrived to be photographed and in whose honour (and that of Mrs Beeton) Spurling is serving afternoon tea.

In the tranquillity of her shady garden, I struggle to imagine the assured Spurling feeling ruffled - let alone panicked. But, when I recall how researching and writing about 84 years of Matisse's life had consumed 15 years of her own, I wonder how anyone could survive such a marathon. Then there is Hughes, who re-mortgaged her home in order to purchase the love letters that Mrs Beeton exchanged with her fiancé. It occurs to me that there is more to being a biographer than meets the eye. Gripped by the bug for revealing other people's lives, I want, desperately, to know what it is.

For Spurling - whose research took her to France, Russia, America and Tahiti, where she interviewed a lady of 96 who had met Matisse off the boat in 1930 - what makes biography exciting is the journey into an unknown world through a web of lost memories and forgotten relationships. 'When you set out, you have no idea where you are going. It's completely unpredictable, which is why it's so much fun.'

For Hughes, an avid fan of TV detective series, life-writing is an addiction fuelled by the thrill of the chase. 'There are times when you become convinced that your subject is slipping out through the back door, while you enter by the front. I remember, in one of my madder moments, staring at the material that I'd gathered and muttering, "There is no hiding from me. You can run but you cannot hide."'

Like sleuths unravelling crimes, making biographical discoveries entails months, even years, of grubbing in dark corners for small shards of evidence. To establish the provenance of Mrs Beeton's recipes in her Book of Household Management, Hughes read just about every cookery book she could get her hands on that had been written before this massive volume made its debut. What she found was not merely the odd culinary and stylistic borrowing, but incontrovertible proof that Beeton - who composed her bible not as a redoubtable matron, but as a wide-eyed newly-wed - had pillaged and pilfered on a colossal scale. 'I had a hunch there would be a bit of cut and pasting, because that's the nature of cookery books. But this was more like plagiarism. It was nice to be the person who gave that proof through forensic detection.'

Psychological insight distilled from meticulous research (a process which she likens to clinical diagnosis) enabled Spurling to overturn the art establishment's reading of Matisse's character. 'A leading art historian told me there had never been a biography of Matisse, because he was too dull to be written about. Well, I just couldn't believe that a man who painted works so full of mystery and power could be dull.'

In the event, her findings vindicated her intuition, revealing behind Matisse's public persona a humorous, yet angst-ridden, man who braved his father's wrath and endured years of poverty, self-doubt and public ridicule to wrestle his way to new forms of expression. But the turmoil in Matisse's life was not limited to his art. Alongside the story of the painter's development, Spurling unearthed a gripping family drama punctuated by the upheavals of war, estranged relationships and a devastating scandal from which Matisse emerged an unsung hero.

'When he had to face powerful people, he put on a suit as a kind of armour and protection. So, of course, everyone thinks of him as the man in the stuffy suit', explains Spurling. 'Also, because he was often in opposition to Picasso and Picasso had a colourful love life, people wrongly drew the conclusion that Matisse must have been dull. In my opinion, Matisse's life was infinitely more eventful than Picasso's.'

Both women cite Oxford as an enduring influence that carried through to what they did subsequently. For Spurling, who read English, college life opened up a world of new opportunities. 'Girls of my generation were very restricted. We were educated for marriage, not for careers. At Somerville, we were immensely lucky. The principal was Dame Janet Vaughan [a leading haematologist]. She made it clear, just by existing, that a woman could be the equal of a man.'

For Hughes, who read history, and who hunted through every parish record of every London church until she had discovered Mrs Beeton's date of birth, being cross-examined in tutorials was an excellent, if sometimes painful, preparation for future sleuthing. 'If you're a big picture person, like me, being quizzed and forced to focus on awkward details is fantastically valuable, although, of course, it was a nightmare at the time.'

Both women began their careers as journalists, Hughes interviewing celebrities (which she detested) and Spurling as the arts and, later, literary editor of the Spectator. Originally set on writing fiction, Spurling fell into biography by chance. At a lunch to discuss Gollancz's spring list, she rounded on the publisher's representative for neglecting one of her favourite novelists, Ivy Compton- Burnett. When Compton-Burnett died, Gollancz invited Spurling to write her biography. The subsequent book, which delved into the domestic traumas that fed Compton- Burnett's novels, established Spurling at the forefront of a band of young biographers determined to liberate their craft from the polite evasions and cover-ups of the past. 'We were like the fearless young bride in Duke Bluebeard's castle. We rushed around flinging open doors and revealing ghastly secrets. The revolution of my generation [Spurling mentions Coleridge's biographer Richard Holmes and Michael Holroyd as comrades in arms] was a reaction against the short facile biographies of the time, which had become very divorced from the reality of people's lives.'

In a Sunday Times article, Spurling once described the revolution that she and her contemporaries ignited as ushering in a 'golden age,' which revitalised biography and raised its intellectual status. A generation later, Hughes is a beneficiary of that legacy, which she came to through a love of history.

In her teens, Hughes drank in the imagined worlds of historical novelists such as Jean Plaidy and Mary Renault. Once at Oxford, however, she discovered that the vivid personalities of the past played second fiddle to the discipline of macro-historical forces and analytical scrutiny. Now, as the Professor of Life Writing at East Anglia University, and in her books on Victorian governesses, George Eliot and the semi-mythical figure of Mrs Beeton, Hughes strives to unite empathy and intellect. 'I felt there had to be a way of doing history that would bring together the wonderful critical insights that we were pushed to develop in tutorials with a sense of putting flesh on the past. What intrigues me is inhabiting another person's life, asking what it must have felt like to be a Victorian governess or a nineteenth-century manufacturer.'

Forty years after Michael Holroyd's ground-breaking biography of Lytton Strachey, which exposed the wayward sexuality of the Bloomsbury circle, Spurling believes that her contemporaries' zeal to lay bare every twist and turn in their subjects' lives has run its course. This she notes as a matter of fact, not a cause for regret, even if it relegates her own monumental life of Matisse to the status of an honoured dinosaur. 'The revolution that we made for complete disclosure was very necessary; but now the detail is getting the better of the pattern [of subjects' lives].' So, if the mighty tome is dead, what will take its place?

For her next project, Spurling plans a 'very short' book - something that doesn't engulf her in reading acres of correspondence. 'My second subject [Paul Scott] left 12,000 letters. He was a father confessor to his friends, so they were full of secrets - but not his.'

As a critic and writer, Hughes scents an opportunity to experiment with biographical forms that focus on facets of lives, or which blend biography with historical analysis and the freedoms of literary expression.

'Biography has always been incredibly playful and flexible', says Hughes. By way of illustration, she cites Boswell's Life of Johnson and also Virginia Woolf, who explored class and gender through the story of Flush, Elizabeth Barrett Browning's dog. 'It's only recently that we've become locked into thinking that biography means dutifully following a life from the cradle to the grave.' As one revolution breathes its last, another is taking its first faltering steps.