There is a passage towards the end of Raj Patel's book, Stuffed and Starved, which elevates its author to the rank of soothsayer. He wrote it at the beginning of 2007, well before the roar of anger about rising food prices that resounded across the planet and that he so uncannily and accurately predicted.

The passage begins with Patel's summary of earlier sections of the book in which he depicts the wasteland, as he calls it, of the modern food system. It is a system that destroys rural communities, poisons poor city dwellers, is inhumane to animals, demands unsustainable levels of use of fossil fuels and water, contributes to global warming, spreads disease and limits our sensuousness and compassion. As if that litany wasn't enough, he then adds this: "Perhaps most ironic, although it is controlled by some of the most powerful people on the planet, the food system is inherently weak. It has systemic and structural vulnerabilities that lie close to the surface of our daily lives. All it takes to expose them is a gentle jolt."

When he wrote that passage, Patel had in mind his native Britain and its occasional history of food crises. There was the oil crisis of 1973 that prompted panic-buying in the shops. Or 2000, when protesting truckers blockaded the oil refineries and the shelves again came close to emptying. Those events inspired Patel to contemplate a startling question: "What would have happened," he wrote, "had all the food on the shelves run out?"

He left that question dangling in the book. But he got thinking about it again as he was on a tour of Australia last August promoting the book. As he travelled from Perth to Melbourne and then Sydney he kept being asked the same question: how did the drought that by then was already biting hard on Australian farmers as well as on consumers who were suffering rising prices, fit into his critique of modern food production? As he faced his audiences, it began to look to Patel, in a tentative, creeping way, that the gentle jolt he had written about was really happening.

"What was weird was that the stories I was hearing about drought and farmers in desperation were very similar to the stories that had been told to me in India a couple of years before. They were all about small independent farmers up to their eyeballs in debt. They had borrowed hugely to make a go of it, and then there'd been a shock - in Australia it was drought, in India it might be harvest failure, in Britain foot-and-mouth. It only takes one small shock."

And then the agricultural slurry really hit the fan. The first intimations of something truly out of the ordinary came in Mexico in early 2007, before he had finished writing Stuffed and Starved. There were reports of unrest in some of the larger cities about rising food prices, partly related to the decision of the US government to divert huge quantities of corn to ethanol production, in an attempt to reduce dependence on foreign oil. Then early this year some eight months after Patel had finished writing about the risk of gentle jolts - the so-called "silent tsunami" began. Food prices appeared to be out of control, spiralling up by 68% in the case of rice in the first four months of this year alone. Wheat and corn almost doubled in a year.

Such hikes on the costs of the basics of life hit the urban poor in the cities of the developing world hardest, and the misery was soon made manifest in the form of unrest. Impromptu protests grew into angry marches and then erupted into food riots. In Haiti six people died and the prime minister was ousted from power. Two days of rioting ensued in Egypt and 24 people died in Cameroon. The pattern repeated itself right across the developing world, from Guyana and Bolivia to Ivory Coast, Surinam and Senegal, Yemen, Uzbekistan, Bangladesh and South Korea. Wild events in turn prompted wild official responses. Vietnam introduced a night curfew on harvesting machines to stop illegal raiding of the fields; any Filipino caught hoarding rice was threatened with life in jail, Malaysia cancelled all public building works and switched instead to stockpiling food. Even the rich western world was hit. Food prices in the UK have risen almost 7% year on year, shaking the government's economic confidence. And if any doubts remained about the severity of this crisis, Wal-Mart, the supermarket goliath that stands at the pinnacle of the modern food system, announced it was imposing a four-bag limit for rice on its cash-and-carry customers to stop a run on supplies.

For millions of people around the world the soaring prices have spelt disaster - the World Bank has put the number of people who have been pushed into hunger at 100 million. But for one person, the impact has been strangely and paradoxically counter-factual. When Stuffed and Starved - Patel's first book - came out last August, he and his publishers imagined it would at best enjoy a specialist readership among globalisation activists attuned to issues of corporate greed and exploitation. But the food crisis has turned it from being a niche read into the literary equivalent of a crystal ball. As a result, the demand has in Patel's words "gone bonkers". Reprints have been ordered in Britain, the US and Spain, deals done for editions in Italy, China and South Korea and half a dozen translations are under discussion. "If I had been this popular at school I'd be a different man today," he quips. His analysis of the crisis, as the author of the book that predicted it all, is now hotly sought after. Or as Patel, who has the savvy Londoner's gift for self-deprecation, puts it: "Spank me, and call me Cassandra!"

We meet for lunch in a restaurant within a Big Mac's throw from Capitol Hill in Washington. It's trivial I know, but it's impossible not to be curious - a little intimidated even - about what Patel will order from the menu. He points out in his book that the livestock industry is responsible for 18% of greenhouse gas emissions, more than cars. So will he go for the hanger steak?

He asks for a pizza with goat's cheese and mushrooms, but when I ask whether his choice was politically or ethically motivated, he laughs. "I haven't had a steak in my life. Growing up in a Hindu household, I clamoured for hamburgers like any other kid and my parents said: 'Oh, if you must.' But they drew the line at steak."

Patel sees in himself, and his eating habits, a tale in microcosm of the globalisation he writes about. His family on his mother's side were civil servants in Kenya, and tin miners in Fiji on his father's side. They both were drawn to the mother country, arriving in London in the 60s, where they met. It later became a cliche, but they were among the first to open up "Mr Patel's corner shop", working 18-hour days in an era before 24-hour supermarkets. The earliest memories of their son, who was born in 1972, are of playing among the fags, mags and sweets in the shop in Golders Green. It would be too neat, I hazard, to suggest that his parents were forced to close down the shop because of competition with the supermarkets? "My dad did very well for himself," he replies, speaking with a high-velocity stammer. "But they were certainly driven out. You can't compete any more, the corner shop is a dying industry."

Despite those difficulties, the Patels did proud by their son, sending him to a north London grammar school, then to Oxford where he studied PPE, and finally to Berkeley in California. Along the way, he became interested in, and engaged with, the anti-globalisation movement. He was among the thousands who protested in Seattle against the World Trade Organisation (WTO) in 1999, and it was there that he came face to face with what he calls the "march of the farmers' movement" in the form of arguably the world's largest network of independent organisations, La Via Campesina, which represents around 150 million farm workers and smallholders across the globe. "I was struck by their sophisticated and detailed critique of the WTO. Seven years before Seattle they had already translated the draft text of the Dunkel report [on trade] into Kannada and were distributing it in the fields."

He began delving more deeply into the subject of trade, food policy and agricultural resistance as an analyst at Food First, a radical thinktank in Oakland, where an idea for a book emerged. It began life as a meditation on choice, or the lack of it - Coke v Pepsi, McDonald's v Wendy's. Its working title was Choice Cuts. Over the next three years he travelled to research the book from South Africa, Europe and South Korea to Brazil, Mexico and the US. In the process the thesis grew bigger in scope and more refined. Its focus was no longer just a lack of consumer choice, it embraced an entire world food system that can consign 800 million - more than one in 10 people on earth - to hunger while simultaneously inflicting obesity on an even greater number, 1 billion people. Hence the book's new, and in his opinion better, title.

His analysis shows how communities around the planet have been disempowered by a system that appears to offer an abundance of cheap food, but in reality dictates unhealthy and limited choices to an overworked and underpaid workforce that cannot afford any better. "The figure that often stuns people outside the US when I tour with the book is that 20% of American fast-food meals are eaten in cars. People are incredulous and ask: is that because Americans so love their cars? But living here you see how hard people work, for a pittance, with no healthcare, no decent education, not even a hint of a pension - so it's not surprising that the one hot meal you eat a day you eat off your lap. That's where the food system becomes a lifestyle."

Much of the broad argument in Stuffed and Starved will be familiar to those who have followed the debate on globalisation - how the liberalisation of trade has created a vast global market for heavily subsidised American and European agricultural products at the expense of local growers in the developing world; how relentless pressure to drive down food prices over 30 years has seen rich ecosystems replaced by monocultures that rely on oil-powered machines, chemical fertilisers and pesticides to drive up yields; and how international corporations and supermarkets that control the flow of technologies and of food itself have been the beneficiaries. It is a portrait of the agro-economics of the madhouse. "While we think our food is made for us, we are in fact being made for our food," he says.

Take India, which he describes as a storm of contradictions. "India has the most people in the Forbes top 10 billionaires list, but in the past decade the average calorie intake of the poorest has fallen. There are levels of hunger we haven't seen since the British left, combined with the world's highest levels of type 2 diabetes from the pressure of eating too much of the wrong kinds of food."

Or take the UK, where food producers are now less than one per cent of the workforce. The government may be committed to reducing global warming emissions, but meanwhile a quarter of all trucks on UK roads are carrying food and the average British family is driving 136 miles a year to buy it.

Or America. This is the country whose farmers, food giants and supermarkets benefit most from the global system. Such is the might of US food corporations that the double arches of McDonald's are more widely recognised as a symbol than the cross. Wal-Mart is the largest private employer not only in the US, but also in Mexico where Walmex takes in three out of every 10 pesos Mexicans spend on food. Yet amid such largesse 35 million Americans don't know where their next meal is coming from. "You are hearing these amazing stories of working American families adopting coping strategies that I learned about in development sociology - skipping meals, growing their own fruit and vegetables, giving up on meat. That's happening right here right now."

Which brings us back to the current food crisis. What surprised him, he says, is not that the food system felt a gentle jolt - after all, he predicted it - but that it has been pummelled all at once by a perfect storm of troubles. "We could have seen it coming because of the biofuels policy, which has always struck me as absurd, or the rising price of oil, or increased consumption of meat, or weird things happening with climate. But all these things happened at once, and that sent food prices through the roof."

And this time, there were none of the safeguards of grain stores, strategic food reserves, or import barriers that used to protect vulnerable economies from the vagaries of world markets. They had all been removed in the liberalisation craze of the past few decades.

His prognosis is that in the short term at least the crisis will carry on biting. Major institutions such as the World Bank persist, he says, in responding to events with the same failed policies of liberalisation of markets. "There's no reason why food prices should come down significantly. And if they don't, and there's no real impetus for governments to redistribute spending power, people will continue to take to the streets."

In the medium term, he's confident that change is in the air. He detects a growing seriousness and willingness to embrace new ideas in some unexpected quarters. The reason we are chatting in a DC restaurant is that Patel has just that morning been giving testimony before a Congressional committee investigating the World Bank's approach to food and development. With representatives from the World Bank, UN, Monsanto and other monoliths listening in, he told the committee that industrial agriculture could no longer be relied upon to feed the world and that we need a shift towards less fossil-fuel dependent farming and a return to rich ecosystems based on natural crop rotations and organic fertilisers. "Those are the kinds of things that are anathema to the World Bank and development analysts at the moment, and Congress normally doesn't want to hear them. That they called on someone like me is very weird, but very heartening."

In the longer term, though, even the current food crisis may seem mild. The world population is set to rise from about six billion today to nine billion by 2050. Global warming is likely to disrupt growing patterns and extend drought across Africa and the American south-west. Water resources for irrigation will be depleted. If we are already in a perfect storm, then we lack the terminology to describe what lies ahead.

I put it to him that any attempt to change world food production is like a game of poker with extraordinarily high stakes: it not only has to meet the massive yield of industrial farming - and say what you like about the modern food system, the one thing it has done is churn out mountains of the stuff relatively cheaply - it also has to raise it to support three billion extra hungry mouths. Can his alternative model achieve that?

"We've got an energy problem, a fuel problem, a water problem and global warming all coming at us," he replies. "Monoculture is heavily C02-emitting, water and fossil-fuel dependent. Clearly we can't carry on as we are. We can and we must meet this challenge with something new. So the question is what?"

That's not entirely an answer to my question. There is a slightly starry-eyed quality to Stuffed and Starved that is also striking about its author in the flesh. When he talks of alternative farming techniques that offer a way forward, the examples he chooses come from Cuba, Venezuela and a project in Oakland that follows in the footsteps of the Black Panthers. That's hardly going to play well with sceptical American policy-makers.

The other element that is lacking from his prognosis is any role for science and technological innovation in the search for solutions. Where technology does appear it is in the role of villain - GM crops are a ruse by Monsanto and others to secure corporate profits at the expense of the rural poor.

But isn't there a place for responsibly directed science in steering us through the coming maelstrom? Couldn't GM, for instance, prove to be crucial in developing drought-resistant crops as global warming tightens its grip?

"I'm big on science, married to a neuroscientist, I love it," he insists, protesting perhaps a little too much. "I like the way Cuban science approaches the problem. They say you can have GM crops if you can prove there's no better way of doing things. So they don't have GM crops, because there always is a better way."

Not exactly a ringing endorsement for the value of science. But then that is not where Patel's heart lies. For that you have to look to politics, and political resistance. The soothsayer's next book, he says, will be a look at the individuals and communities who are refusing to bow down to the current global system. He will soon be starting another journey to meet them. On his list: the slum-dwellers of Durban and the homeless Americans who run the University of the Poor. He sees in them a lesson for us all. "We are victims," he says as he polishes off his pizza and prepares to fly back to San Francisco where he now lives. "If we are choosing between Coke or Pepsi, Burger King or McDonald's, that's not choice. We should stop feeling guilty about that. We should start feeling angry".

· Stuffed & Starved is published by Portobello and available from the Guardian bookshop at £8.99 + p&p