It is early summer in London and The New Yorker is gathering India’s leading novelists in one room for a monumental photograph. What is remarkable about the occasion, apart from the exclusion of any writer not working in English, is the prominence given to Arundhati Roy. She stands at the front of the group, squeezed between Vikram Chandra and Anita Desai, laughing playfully as Salman Rushdie rests a supportive hand on her shoulder. It is as if the older writer, who himself did so much in Midnight’s Children to redefine the boundaries of the Anglo-Indian novel, is bestowing a special favour on the younger Roy, marking her out. Long before her Booker triumph Roy, a minor screenwriter, has published no fiction. So why is she in the photograph? To call her one of India’s leading writers is surely a crass exaggeration, a triumph of marketing and media manipulation over literary substance. For she has nothing to declare except a spectacular advance for a novel which scarcely anyone has read, but which, according to Pankaj Mishra, the young Indian publisher who discovered Roy, is “the biggest thing since Midnight’s Children “. Certainly, there was unprecedented interest in The God Of Small Things ; the English literary agent David Godwin flew to India to sign up Roy within four days of receiving her manuscript. Can the book be that good?

Time moves on. Arundhati Roy, in London for the Booker Prize ceremony, greets me in the imperious entrance of St James’s Club, Piccadilly, with a shy smile. Four months have passed since The New Yorker photograph and she is just back from a promotional trip to Finland and Estonia. She is full of excitement and baffled delight at the success of her book. She is 37, but could be ten years younger.

In the listless heat of a Delhi afternoon Roy sometimes lies in her apartment listening to the mechanical thwack of a ceiling fan and thinking, as she puts it, about “the rest of the world at work”. For she has the fabulous luxury of never having to work again. Her novel has been sold to 30 countries, earning in excess of Pounds 1 million in advanced rights sales. It is high on the bestseller lists in the US, India, Australia and Britain. In Bombay, it is even being sold to motorists as they wait at traffic lights.

The God Of Small Things is set in Kerala, the southern Indian state where the world’s great faiths collide: Christianity, Hinduism, Islam and Marxism. The main action takes place over a fortnight and concerns the drowning of an Anglo-Indian girl, Sophie Mol, on holiday from England. Sophie, befriended by the twins, Estha and Rahael, through whom the narrative is refracted, spends her holiday in a rapture of discovery. She explores the hot, lush waterways and meadows of Kerala, and encounters Velutha, a despised Paravan, the lowest of the Untouchables, with whom the twins’ mother, Ammu, has a doomed affair.

Though the ending is flagged as early as page four, Roy allows events to emerge elliptically and out of chronological sequence. An atmosphere of foreboding hangs over the work. It is immensely absorbing.

Roy’s journey, in less than a year, from putative novelist to global literary phenomenon is almost as magical and unexpected as her fiction. She must have given many interviews - she says she is “hounded” in India - yet still speaks about her life-transforming experience with the vitality of a child.

And there is something childish about Roy. It is not that she is immature; it’s rather that she has a heightened capacity for wonder, seeing the world as a child might, not conventionally or habitually, but as if for the first time. This accounts for the defamiliarising quality of her prose, her metaphorical exactitude and striking similes: a moonlit river falling from a swimmer’s arms like “sleeves of silver”; the smell of shit hovering over a village “like a hat”; conversa tion “dipping like mountain streams”.

Where did it come from, this verbal exuberance? “My language is the one thing I’m least equipped to talk about,” she says, sitting at a round table in a room presumably used for business meetings - there are blotters, sharpened pencils, bottles of water and notepaper on the table. “My language,” she continues, “is entirely instinctive. It is the skin of my thought. I crafted and designed the book’s structure obsessively for four and a half years, but the language was natural. It came easily, even though I don’t know much grammar.” She teases, surely?

Roy is diminutive, not much more than 5ft, and her legs scarcely touch the ground. As she talks her face is never still. A small diamond gleams in one nostril, catching the light. Like the twins in the novel, Roy grew up in Kerala, the daughter of a Christian mother and Bengali Hindu father. Her parents separated when she was a young child. Her adolescence was difficult; she clashed continually with her mother, Mary, who worked as a teacher, testing her progressive ideas on her rebellious daughter. Roy was forced to leave home when she was 16; for six years she never spoke to her mother. Yet the novel is dedicated to Mary Roy, the mother who “loved me enough to let me go”.

After training to be an architect in Delhi, Roy became interested in film, working as a designer and on scripts. She met her husband, Krishen, who has two daughters from an earlier marriage “by accident, on the street”. They collaborated on a film, Electric Moon , commissioned by Channel 4 in 1992.

Reflecting on her restless years, she says: “Everything I did back then I did to be happy. After being turfed out of home I had to earn my own living, so I feel as if I am about to live my teenage years for the first time. What happened at home was traumatic and bad; it has left me terrified of conventional families.”

What is most admirable about The God Of Small Things is Roy’s attempt to invent her own idiom, to be first with a new way of writing about modern life. There is a powerful sense of language being mangled, stretched and distorted. She has an acute sensitivity to the natural world, filling her pages with smells and sounds, colour and light, with the “small things” of life that are so easily devoured by habitualism.

Reading her erratic, burnished prose you realise that here, at last, is a novel not in thrall to the past. John Updike is right when he likens her to Tiger Woods: there is something seriously freakish in her. Some thing Woodsian. “I was amused when Updike said that about Tiger Woods,” Roy says, laughing, “because I had no idea who Woods is. When people told me I was very flattered.”

Yet her novel has many enemies. The critic Peter Kemp, irritated by her inclusion on the Booker Prize shortlist, continually bemoans what he calls her “typographical tweeness” - archly capitalised phrases, coy mispellings, a liberal sprinkling of italics. Salman Rushdie, though praising her vevre and ambition, is disappointed by her refusal to describe India as exotic. And in India itself, she has been criticised for working in English and for having too much money, as well as being accused of obscenity for describing cross-caste erotic love between a Paravan and a Syrian Christian.

The question of money troubles her. “In India I have spent my whole life feeling so horribly guilty about how much more privileged I am than almost everyone else - and this when I had nothing except an education. So I find what has happened to me and the money I’ve got a kind of ghoulish reward. It’s very easy for people to say, ‘Okay, give it away’. But in India you can’t just go into a poor village and say, ‘Here’s some money’. You can screw things up like that. If you give money away you must do it properly, to ensure that it gets to the right people.”

For Rushdie, in unhappy exile in London, India is “vast, metamorphic…a non-stop assault on the senses, the emotions, the imagination and the spirit”. In short: an exotic land of magic and extremes. As a result, his work is resplendent with flying men, talking noses and the other gimmicks of magic realism. But for Roy, whose work is grounded in the actual, there is nothing remarkable about India. To her reality is magical.

She says: “When I was in America I went on a couple of TV shows with Rushdie. And he said, (she borrows the voice of an officious schoolmaster) ‘The trouble with Arundhati is that she insists that India is an ordinary place’. Well, I ask, ‘Why, the hell not?’ It is my ordinary life. The difference between me and Rushdie begins there.

“I don’t want Brownie points because I’m from India. My book doesn’t trade on the currency of cultural specificity, even though the details are right. That is why, I think, it has been bought in so many countries, and why Americans come up to me and say, ‘I’ve got an aunt like Baby Kochamma’ ” (a malign character, who schemes to destroy Ammu and the twins).

In June, shortly after the publication of The God of Small Things , Roy hinted that she might never write again. Exhausted by her striving, she had “nothing more to give”. Does she still feel that way? Her answer is oblique and surprising.

“Ever since I was quite young I have not believed in professions; I don’t want to say, ‘I’m a writer and so I’m going to write another book. I will only write another book if I feel I have one to write. People should respect that you are creatively exhausted after a novel. I get irritated if a publisher tries to get me to sign another contract.”

She is surely right. Perhaps it is unreasonable to expect more from her than this one small wonder of style and compassion. She deserved to win.