Arundhati Roy has two voices. The first, dramatically personal and playful, was the one in which she wrote her extraordinary debut novel, The God of Small Things, a semi-autobiographical account of growing up in rural Kerala. The second voice is flatter and angrier, more urban and distrustful of the quirks of the individual. She describes it as "writing from the heart of the crowd". It is this voice that she has used exclusively in the 12 years since her novel was published, in four collections of non-fiction - the latest of which, Listening to Grasshoppers: Field Notes on Democracy, was published last week.

Roy, now 47, describes the difference between the two voices as the difference between "dancing and walking". It is a long while since Roy's writing has danced. She says she pedestrianised her imagination not out of choice, not at all, but because there seemed nothing else to do. "If I could," she says, "I would love to spend all my time writing fiction. With the non-fiction I wrote one book that I wanted to write and three more that I didn't."

This compulsion - towards reporting and polemic - Roy blames in part on the success of The God of Small Things. She wrote her novel for four and a half years entirely in secret; even her husband, the film-maker Pradip Krishen, did not know of its existence until it was finished. And she wrote it for herself. She had written a couple of film scripts before that and had come to despise the collaborative creative process. The book was an exercise in downshifting. She imagined when it was published that it would sell "maybe 500 copies in Delhi." In fact, it sold 6m copies worldwide and won her the Booker Prize.

"The prize," she says now, "was actually responsible in many ways for my political activism. I won this thing and I was suddenly the darling of the new emerging Indian middle class - they needed a princess. They had the wrong woman. I had this light shining on me at the time, and I knew that I had the stage to say something about what was happening in my country. What is exciting about what I have done since is that writing has become a weapon, some kind of ammunition."

The essays in Listening to Grasshoppers are her collected hand grenades from the last eight years. Roy says the process of putting them together has been "totally sad for me in a way - to see that six years ago you said something was going to happen and then it happened. It is not as though I am a genius or a witch. When you start seeing the way the whole machine works, the structure of what is happening is so clear."

That machine is the engine of free market "progress" that politicians in Delhi call "Indian Shining". Roy sees it as the destruction for multinational corporate profit of everything that her nation should care about. Her book begins with a question: "Is there life after democracy?" and goes on to count the ways that successive Indian governments and businessmen have waged a repressive war on the poor and on minorities, and have pursued devastating environmental destruction for economic and political gain.

She has just returned from the Chhattisgarh region, which is "being targeted by corporates for its wealth of iron ore. In the name of fighting Maoist rebels, hundreds of villages have been forcibly evacuated and almost 40,000 people moved into police camps." It is, she says, heartbreaking to see what is going on, "the levels of violence, the levels of dispossession; if that was happening in Iran or some other country that didn't have a free market and a democracy it would have been on the front pages every day. Because it is India it does not rate a mention."

In her stride, she goes on to describe the "building of a hundred dams in the high Himalayas. When you see what is being done it is like it is being done to your own body." In 2002 Roy was briefly imprisoned for her protests against the Narmada dam project. When she talks of these things now - and of the horror of the ongoing war in Kashmir - it is with a rawness and a weariness that makes you half-expect her to scream with anger.

"Time is running out," she says, "rivers are running dry. But you cannot fight against dams. It doesn't involve just people; it involves a whole eco system and cropping patterns. But you cannot have an armed struggle against a rising river."

While the Indian miracle takes place, she says, the country is host to more than a third of the world's undernourished children. Only her compatriots could have celebrated the victory of Slumdog Millionaire on Oscar night. "The fact that the film - not even an Indian film - won these prizes sent people into orbit. But it is an odd movie for a country to be proud of. What were we celebrating? Child poverty? If it wasn't so tragic it would be comical."

When I ask her where she places her hope, Roy shrugs. She is tiny in stature, but her disillusion can fill a room. She has no faith in conventional politics to change anything. Obama "might be a symbol," she concedes, but nothing "about the relation of American capitalism with the rest of the world will alter ... To answer your question, it's not about my hope, it's about my DNA. There are people who are comfortable with power and people who are distinctly uncomfortable and made to question it."

In this respect, Roy is very much her mother's daughter. Before Arundhati was born, Mary Roy was a visible and vocal campaigner for women's rights. As a divorcee she set up an experimental girl's school; Arundhati was her star pupil. Does she feel like a creation of her mother? "No. We are temperamentally very different," she says quickly. "My mother runs a huge institution; she has hundreds of people working for her, and I am completely a loner, I don't even have a secretary or anybody. I am almost terrified of that. In my head I want to feel I can be anywhere. There is a sort of recklessness that being a loner allows me."

Roy left home as soon as she could, initially to become an architect and then to follow other dreams. "When I was 18," she has written elsewhere, "I chose freedom over the safety of a home, good clothes and Johnson's baby lotion. The fortunate thing was that I didn't need to be married, or oppressed, or beaten to decide that I wanted independence at all costs."

Roy speaks a lot about her activist mother but her father disappears from her story. What became of him? "My parents separated when I was two, and I never saw my father until I was 24 or 25," she says. "He was an alcoholic, completely. He died last year. I didn't really know him but I was there at the end. My aunt used to look after him and I used to help sometimes but you couldn't talk to him, not really..."

She must have felt that as an absence? "I think that in some ways," she says, "the fact that my father was missing from my life was not a bad thing. For one thing it gave my mother a lot of space to indulge her personality, and she needed at least enough space for two people! And it allowed me to avoid any kind of paternal battles. Just by experience I was a natural born feminist, I didn't have to be schooled. That is how it was."

Roy made a decision quite young not to have kids. Was that another strategy to protect her freedom? "Well in a way, growing up, I had always had kids. At my mother's school - when I was four I was looking after kids who were three. I did quite a lot of teaching. By the time I was 16 I never wanted to see another child again!"

She draws strength for her struggles from other writers; Noam Chomsky, John Berger are names that crop up repeatedly. "I see them occasionally, I read them. There is a shared affection I think."

If she hadn't won the Booker Prize, does she believe she would have written more novels by now? "I have no idea if I would have written more or less or none at all," she says. "But it did change things. Now I feel that I am ready to do it again, in some ways, but I am not finding the space. It is a difficult choice for me when there is always something happening. In a philosophical sense I know I am insignificant, but in the current moment I can make a bit of a difference." That belief makes her a constant irritation to Indian politicians; she is the scourge of the Hindu nationalists, of the BJP in particular. She rather relishes the role.

"For the past decade or so they have tried both ways to keep me quiet," she says, smiling." They have tried putting me in prison and they have tried giving me awards. In the run up to these elections the home minister LK Advani was mentioning me by name at rallies, you know, denouncing me as an anti-national ..."

I suggest to her that part of the freedom she covets is perhaps the freedom to fail; I have the sense, talking to her, that she distrusts intensely the idea of herself as a literary icon. "It is true," she says, "that success is the most boring thing, it is tinny and brittle, failure runs deeper. Success is dangerous. I have a very complicated relationship with that word. I think that I was quite a grown-up child, and I have been a pretty childish adult. When I was very small this mad uncle of mine who is one of the main characters in my novel took me on one side and showed me this horrible bauble. He said 'Do you want this?' I was maybe three or something, and of course I did. He said, 'Well I will give it you as long as you promise to fail.' That idea has certainly stayed with me."

It is hard, talking to Roy, to see where she finds the joy in her life that glittered in some of the sentences of her novel. Her husband has just written a book about the trees of Delhi, which has become a surprise bestseller. Is that a passion they share?

They have, she says, a different relationship to nature. "He was a person who grew up in Delhi and I grew up on the river in Kerala. I was frightened of being stuck there and married off to some dull Syrian Christian boy so I used to dream always of escape to the big city. My husband's dreams went in the other direction."

So they have found common ground in their city's trees? "He is a much more methodical person than me, he likes to name things. If I go into the forest I can appreciate its beauty but I almost immediately want to know the politics of it. I want to know who is buying the mangoes, what is under the ground."

As we talk, Roy from time to time expresses her concern not to be presented as a personality. "You know, this is not the life of Arundhati ... I have no interest in that at all." She hates to be boxed in, she suggests, even in a profile. Does she worry, I wonder, about losing the smaller voice, the individual one?

"Well, if I lose it, so what?" she says. "I am writing bits of fiction but then I get derailed by something happening."

Does she ever think a novel might sometimes be a more affecting way to express her politics? She says she doesn't know. And then she goes on to describe the brutal economics of bauxite mining in the state of Orissa.

Arundhati Roy: A Life

Born Suzanna Arundhati Roy in 1961, in Meghalaya, India, to a Keralite Syrian mother, women's rights activist Mary Roy, and a Bengali tea-planter father.

Studied at the School of Planning and Architecture, New Delhi.

Married architect Gerard da Cunha in 1977. She divorced him after four years, and later married film-maker Pradip Krishen, whom she met in 1984 while appearing as a "tribal bimbo" in one of his films.

Career Screenplays including In Which Annie Gives It Those Ones (1989) and Electric Moon (1992). Began The God of Small Things in 1992; won the Booker Prize in 1997.

Political works include The Cost of Living (1999) and The Algebra of Infinite Justice (2002). Is an outspoken critic of US foreign policy, India's nuclear weapons and the conduct of Israel, and a supporter of Kashmiri independence.

Awarded the Sydney Peace Prize in 2004.