Jenny Diski has used her life on the edges of insanity to great and frightening effect in her novels. Ajay Close finds her only need now is for a good degree of solitude.

Interviewing Jenny Diski is a bit like getting to know someone in reverse. You start by reading her books and journalism, full of the funny-sore self-analysis women go in for once they have taken the decision to become lifelong friends. Then you actually meet her, spend a couple of hours in her home and, on leaving, feel it would be presumptuous to reach out and shake her hand.

I knew it would be like this, of course. I’d read Stranger on a Train, her memoir of two rail trips across America - though the real journey is into Diski’s personal heart of darkness. She could have stayed home and written essentially the same book, albeit without the gigolos, missionaries, transvestites, models and drunks. Both journeys were packed with incident. She was propositioned four times, twice with lifelong commitment in mind. Her train hit a car, killing two of its passengers. Yet the biggest drama in the book is a paranoid fantasy inside her own head: a kidnapping which never happened and was never likely to, but which had her utterly terrified. The trigger? Accepting an invitation from an acquaintance she met on the train, and spending five days at her home in Albuquerque.

"I’d stopped moving, meeting and withdrawing from people," she writes. "Just five days, not even a week, and I was beside myself with terror that I was trapped, that I would never get away from people ... To be staying in a house with a family was to be engaged in a way that I found nearly intolerable, actually dangerous."

Intimacy problems are a cliche of the 21st century. We all know someone who has trouble with commitment, we’ve seen the talk shows and the episodes of Ally McBeal. But Jenny Diski is in another league. She calls it "separateness" and, one way or another, it has furnished her life’s work. Not that you’d guess it, meeting her socially. She can do parties, engaging conversation, laughter - then she’ll come home and go to bed for two days, stricken with self-disgust. She’s the perfect interviewee: candid, humorous, relentlessly intelligent, highly likeable. But not warm.

Diski lives in Cambridge, but really she’s a Hampstead intellectual. She tries to get away with the label "Hampstead frock-shopper" instead, but concedes: "I’m a sort of liberal lefty wet human being who thinks things ought to be quite nice in the world." There’s more to her qualifications than that. Not every liberal lefty has Diski’s hyper-articulate fluency. Not every liberal lefty has written eight novels, a book of short stories, two book-length memoirs, a collection of essays, and contributes regularly to the London Review of Books. Not every liberal lefty had Doris Lessing as a foster mother and lived in a household where RD Laing was a regular dinner guest. "We were all sent round to the Tavvy," she says at one point, referring to Hamsptead’s famous centre of Freudian analysis, the Tavistock Institute, in the careless way that Glaswegians speak of "the Co".

But that was in her teenage years. What came first was much less comfortable.

She was the only child of a Jewish couple in the East End of London. Her father, whom she loved, was a black-marketeer during and after the war. Later he made a living by seducing women who had money. A real con-man, she assures me, matter-of-factly: "He’d gone to prison at some time." Her voice rises into the register of wonder. "He had an office." When reviewing Diski’s early life, it’s the touches of normality which surprise.

She would lie awake at night, listening to her parents’ screaming matches, hearing knives being taken out of the drawer. When she was 11 her father walked out for the last time. Diski was left with her mother, whom she hated. Though hate may be too weak a word. "I only have a kind of monster mother, really. I’ve done that thing: trying to think about the good things about her. She had a story she used to tell me, she had a joke - only one, but she had a joke. She was terribly concerned about me, as it were …" She gives up. "I find it so hard to really accept anything positive about her."

She must have had all sorts of nice qualities, but her daughter just can’t imagine them. A couple of people who met her have told Diski they found her completely terrifying and crazed. "She was really quite unpleasant to me." "Unpleasant" means ranting and raving, a woman with a history of mental instability who blamed her many disappointments on her daughter and told her she was just like her father: bad through and through. "But what I knew, and I’m talking about six or seven years old, was that I wasn’t bad. I had this little place," she points to a spot in her solar plexus, "it was a little nugget and I could dive down and check it out and it wasn’t bad, it was good." Kids have these funny little things, she shrugs. By the time she was 11 or 12, this secret kernel of goodness was gone. "I resolved then to be what I was supposed to be, I guess."

It’s hard to say which is the more upsetting: this vignette of the 11-year-old brainwashed into "badness", or the Ken Loach drama of the mad mother who, on being deserted by her husband, refused to claim social security because it smacked of the workhouse. They ended up in an empty flat with one bed and one chair, everything else having been taken by the bailiffs. The mother was not capable of resolving the situation, so the daughter took action. "I freaked out and they sent the social workers in." She got what she wanted: away from mum. Having a high IQ, she was sent to a progressive co-educational boarding school.

Being bad wasn’t all bad, it was also exciting - climbing out of her dormitory in the middle of the night, going to parties, drinking poteen - but it led, predictably, to expulsion. She went to live with her father and his new lover. They too threw her out. She ended up, at the age of 15, in a psychiatric hospital, not because she was mentally ill, but because nobody knew what to do with her.

Being in the bin was fun in a way, she says. She’d go for her sessions with the shrink and they’d sit in silence. "He’d say ‘have you got anything to tell me?’ and I’d say ‘no’." Out of the blue, she was fostered by Doris Lessing, whose son had been a fellow pupil at the boarding school. It should have been happy-ever-after, but the very randomness of the rescue was a source of stress. On the ward she had experienced for the first time a qualified sense of belonging. Plucked out of hospital, she suffered from survivor guilt. In 1966 her father died unexpectedly. She left school without sitting her A-levels, went to live in a bedsit and spiralled into depression. Her late-adolescence is a harrowing chronicle of drug-taking (with and without prescription), spells in and out of psychiatric hospital, and suicide attempts.

And then the drugs and the madness came to an end. "I just decided that I probably ought not to spend the rest of my life being a nutcase - though it was a close decision," she says. She took a secretarial course, found she resented making tea for her male bosses, retrained as a teacher alongside Ken Livingstone, taught, got married, had a baby …

Hang on, what about her terror of being trapped, the conviction that she can only truly be herself in solitude? "I wasn’t brilliantly good at being married," she admits. They bought a house and turned it into two flats: Roger lived upstairs, she lived downstairs. "As marriages go, it was well-organised." Then they separated, amicably, and cared for their daughter Chloe on a two weeks-on, two weeks-off basis. Diski always had time to herself. "Had we stayed together it would have been catastrophic," she says. "My solution to life is to get divorced."

Her first novel Nothing Natural, about a sado-masochistic sexual affair, was published in 1986. It was a mildly scandalous success. The critic Anthony Thwaite called it "the most revolting book I’ve ever read" and she was banned by the Islington-based feminist magazine Sisterwrite, but mostly the novel was well-received as a timely exploration of a taboo subject. She received a few salacious enquiries as to whether it was autobiographical - which it was, in the sense that its central character had profound difficulties with love and trust. Isolation, emotional emptiness, fear of intimacy, a fragmented or non-existent sense of self: these are Diski’s perennial themes. In Like Mother she used the disturbing conceit of a baby born without a brain, a child its mother christens Nony, short for "Nonentity". The novel, which recycles much of Diski’s angry childhood, is a bleak, blackly humorous work. Or at least the first 50 pages are. I started reading it after meeting Diski, went to bed, had nightmares, woke up, threw up, and have not been able to touch the book since.

I can imagine the author’s sardonic reaction to this news. Even as she places the most painful material on the page, she remains at one remove from it, a dry, often ironic voice. "I write cold," she said once. And at times she reads cold but, at her visceral best, the reader can only wonder "why isn’t she screaming?"

The answer is, occasionally she does, but never unreservedly. Not long ago she was watching the movie Now Voyager, in which Bette Davis plays the ugly duckling daughter of a monster mother. Diski started crying. It’s a three-hankie movie anyway, but her weeping went over the score. "Suddenly I was completely distorted with tears. I couldn’t stop. It was another sort of crying altogether," she recalls. "I suppose you’d like to think that something very deep was being touched in me about deprivation and madness, but what was also being touched might have been something very sentimental and corny."

She was brought up in a welter of hysterical emotion. "My mother was a kind of joke hysteric, so presumably I withdrew and became a critic. ‘This is a cheap shot’ I’d think, as she said ‘you should have been strangled at birth’." She’s allergic to easy feelings, what she calls "banality". Or else she’s so susceptible that she never drops her guard.

Maybe the critic in her senses her interviewer’s latent sentimental streak, for she starts to argue against the line of her own book: it’s not so awful, not fitting in. Separateness has its consolations. "Maybe in the end I’m so narcissistic that I prefer my own lack of belonging. That’s where I belong: my own exclusive club." Even if it means not trusting others? "People are immensely dangerous, they walk away, say no, betray. There’s part of me that says that’s true, and another part that says ‘what a nuisance it is that I think like that, but there it is’."

But recent events suggest there is also a third, less resigned part of her. Within the last two years she has uprooted herself from London to be nearer the poet and Cambridge don Ian Patterson. She couldn’t quite bring herself to move in with him, but she did buy a house directly across the street. Does this not indicate a radical change of heart? She is quick to stamp on the idea. "I don’t think I’ve changed since I was three-years-old - I might have a bigger vocabulary, but not much bigger. I just think I’m me with the added anxiety of having a relationship. I worry all the time: I think it can’t be right not to have days and days and days when I don’t see anybody, but it’s remarkably easy."

Let’s leave her there. I’m corny enough to prefer a happy ending and - who knows? - somewhere under her hardboiled, hyper-articulate, critical exterior, maybe Jenny Diski is too.