Likened once to a highly-strung racehorse, she seems, initially at least, to approach interviews with as much relish as a visit to a chiropodist.
In London for the day, she has travelled up from Brighton where, after a peripatetic life, she lives. Now in her mid-forties, she is youthfully slim with a curtain of dark hair and an accent that only locates her as middle class. She has been a published writer since 1993, when Saving Agnes won the Whitbread first novel prize. There have been six further novels and three works of non-fiction.
It seems to be the latter which has caused Cusk most grief. In 2001, she produced Life's Work: On Becoming A Mother, in which she documented her experience with unsparing detail, receiving in some quarters the kind of reaction reserved for child molesters. Eight years later came The Last Supper, an account of three months in Italy in search of painter Piero della Francesca and other Tuscan delights with her then husband and their two daughters. Having not taken the trouble to disguise the people she was writing about, Cusk was sued for breach of privacy and her book was pulped, partly at her expense.
"Objectivity" is the word Cusk uses to define her approach. It is as if she is writing about what has happened to her with the cold, clinical, uninvolved eye of a scientist. Thus she becomes a character, a cipher, as do her husband and children. She avoids subjectivity wherever possible, she says, preferring to talk about DH Lawrence and Greek tragedy rather than her own domestic circumstances. "By subjectivity, I mean the grip of feelings that distort reality. I try to find what this reality is. It's the job, I guess."
Which is all very well. But for the prurient among us it is hard to grasp what exactly drove her marriage on to the rocks. What we do know for sure is that when it did end, it did so painfully and with anger on both sides. Cusk compares it to the dismantlement of a jigsaw but that seems too tempered and civilised. The demolition of a house by wrecker's ball may be nearer the truth.
Cusk and her husband, a photographer who stayed at home to look after their daughters, are merely one relatively unknown couple among tens of thousands whose marriage has imploded. What interests Cusk, however, is not so much why her marriage failed, but her reaction to its failure. A marriage, she explains, is an agreement, whereas a divorce is an argument. "Suddenly, there are two warring versions of what happened. Always. I don't think fault comes into it. It's disagreement, it's conflict."
To her credit, she makes no attempt in Aftermath to present herself in a kindly light. On the contrary, she appears to go out of her way to put the case for the prosecution. Her husband, as shadowy a presence here as he was in The Last Supper, is the wronged party, forced to call her to ask for money, as wives normally have to do. He believes, she reports, that she's treated him "monstrously". Nothing she can say will make him change his mind. What she actually does say she doesn't disclose.
"He believed he had taken the part of the woman in our marriage," she writes, "and seemed to expect me to defend him against myself, the male oppressor. He felt it was womanly to shop and cook, to collect the children from school. Yet it was when I myself did those things that I often felt most unsexed."
All of which, Cusk intimates, is symptomatic of the effect on people when something they have not bargained for hits them. The only true way to know how you will react to an event – be it a war , a lottery win or childbirth – is to have previous knowledge of it which, of course, you can't have until it happens, an example of Catch-22. Marriage, like becoming a mother, is one such event. But is her view of marriage ultimately one, as she says in her book, of "entirely unfounded optimism"?
"Do I suggest that?" she laughs. "I suppose what I mean is that you're optimistic about things when you have some reason to believe that they'll turn out well. To be optimistic about something that is absolutely unknown to you is unfounded. I don't mean that it is destined to fail. People have enormous faith in that moment. There are lots of parts of life that operate like that."
Consoling as that may be to future brides and bridegrooms, Cusk adds that in getting married we tend to throw caution to the wind. Why? "It's an institution. It's a form. It's a very familiar form. So that there's a lack of caution about entering it. It feels familiar." For her, marriage, like having children or moving abroad in search of an aesthetically enhanced lifestyle, is a chapter in a life, a subject to address, because it interests her.
In that sense, she uses herself unpityingly, as she does others. All, it seems, is grist to the writer's mill, which is the penalty many must pay for having a writer in their orbit. What is tricky to gauge, however, is the extent to which Cusk is describing real and invented events. For example, did she really invite a mad, drunken lodger to stay with her and her daughters? And did they go on a horrible holiday to Devon where they found themselves imprisoned in a "witch's house"?
Perhaps. But then, perhaps not. For many contemporary writers, reality seems an inconvenient intrusion into an elastic narrative in which what's imagined and what did happen are moulded until it's impossible to tell one from the other. What remains, in Cusk's case, is a sense of surprise. Talking to her, one is struck by the extent to which she can't quite believe how she behaved in particular situations. It's as if she was living in a dwam, unable to anticipate what she would do when she and her husband split up. In Aftermath, her husband tells her he wants half of everything. Her response is an emphatic "no", adding: "You can't divide people in half." When he points out that the children are his too, she counters: "They're my children - They belong to me."
Why, I ask, did she say that? Her reply is illuminating and infuriating, which would be my verdict on Aftermath. "What I was trying to show was that there was a primitive maternalism at the bottom of all this equality and that interested me. And if in fact I didn't say 'no', but just felt it – which may well be the case, I can't remember – it was interesting to me that actually equality, which is the thing I prized the most – not just in marriage but in all my beliefs - that was actually again one of these things, these areas, where knowing something through experience, or just knowing it from some other route are two very different things... It was like going into combat and realising you're a coward. Or going into combat and doing precisely the opposite of what you thought you were going to do."
Aftermath: On Marriage And Separation is published by Faber priced £12.99.