This is a strange place: thousands of acres covered with a single broad-leafed plant dripping with cocktails of chemicals so poisonous that virtually all other life is unknown. There are few birds. Even insects struggle to survive. It is the eerie world of banana plantations - a green desert stretching for hundreds of miles across Central and South America.

Campaigning journalist David Ransom calls it the “dead zone”. When he visited Guatemala in 1999, he found the workers on the huge, pesticide-soaked plantations were doing little better than the insects.

They complained of foul-smelling chemicals being dropped on them from planes, despite promises from employers not to fumigate when workers were in the fields. They talked of the stench as the pesticides evaporated in the mid-afternoon heat and the sicknesses they suffered: sores on their feet, women unable to breast feed, nausea, nose bleeds and blurred vision.

The long-term effects may be much worse. In Costa Rica, estimates of the number of workers made sterile by chemicals that are now banned but were used on banana plantations in the past vary between 1,500 and 10,000 people. The higher figure, published by the leading English-language newspaper in the region, represents about 20 per cent of the workforce.

Women in the packing plants suffer DNAand chromosome deformities, according to researchers at the National University of Costa Rica. These may lead to cancer and birth defects. There are harrowing anecdotes of babies being born with their head four times the size of their body.

None of this is new to the ‘dead zone’. Around 150 years ago, this tragic landscape was covered with tropical forests, noisy with all kinds of life, beside oozing marshlands, mangrove swamps and a coastline boasting some of the most beautiful coral reefs in the world. In 1873, American entrepreneur Minor Cooper Keith arrived with a suggestively curved yellow foreign fruit.

Eve’s innocence was lost to an apple, but Central America’s was lost to a banana.

By the 1920s, the United Fruit Company - the huge corporation that grew out of Keith’s enterprise - had established a vice-like grip over the states of the region, known pejoratively as “banana republics”. The Guatemalan novelist Miguel Angel Asturias described Keith’s power: “He sneezes and president, whether general or lawyer falls... He rubs his behind on his chair and a revolution breaks out.”

Another writer, the Colombian Gabriel Garc!a M rquez, described in his book One Hundred Years of Solitude the gunning down of 400 striking United Fruit workers by the Colombian military in 1929. It was only part of a long history of violent suppression of workers’ complaints. Today, free organisation of unions is still not tolerated on many plantations.

Activists are often sacked and pursued with lawsuits, and some have been killed. The big three banana companies, Chiquita, Dole and Del Monte, which continued North American dominance after United Fruit was broken up in 1954, still make millions from a trade in which employees work 12 to 14-hour days in hazardous conditions for as little as 40p an hour.

One thing living with the banana has taught many Central Americans is not to eat the crop they break their backs producing. When David Ransom asked one Guatemalan whether he ate bananas, the answer was: “Good Lord, no! People in places like this don’t eat the fruit they cut. I guess we know better.” In the supermarkets of Europe and North America, however, consumption of these spotless, chemically farmed fruits is relentless. To understand what is going on in Central America, we need to move to another artificially antiseptic environment: Saturday morning at Tesco’s Extra.

This new glass-fronted mega-market on the outskirts of Cambridge is packed every weekend with people doing their best to get through a necessary weekly expedition with a minimum of hassle. Some will take pleasure from the odd treat added here and there to the trolley but, for most, this is an ordeal to be endured. Few realise it is one of the most political acts of their lives.

It is in these kinds of places that Western consumers, with their huge spending power, decide the way the world will be. Many of these shoppers will spend a fair amount of thought once every four or so years deciding how to vote in a general election. Their one vote among millions is valued highly. It’s a chance to help decide how things should be run. But suggest to the Saturday shoppers that they flex far more power every week through their visits to the supermarket and you will be greeted, as we were in a straw poll in Tesco’s Extra, with raised eyebrows, a grimace and a single knowing nod.

It is hardly surprising. Everything about the modern shopping environment is meant to separate the consumer from the consequences of their decisions.

A cornucopia of products is paraded in front of us, each with their own brand telling a carefully formulated marketing story. (“The man from Del Monte says ‘Yes’.” Cue: hysteria from the brown-faced natives as the white-suited man tips his Panama hat.) Each packaged product contains detailed information about its precise chemical components, often listing them exhaustively down to the last E number. But you will search in vain for information about the social and economic conditions in which the item was produced. Ask the company and you will probably be fobbed off with vague talk about the need for “commercial confidentiality”. The modern supermarket is a fantasy world worthy of Hollywood, in which no decision has any consequence beyond the waistline and wallet of the shopper.

“What we need to do is reconnect people with the real meaning of what they are doing,” says Harriet Lamb, director of the Fairtrade Foundation. “They have been told cheap is best, but somebody usually pays for those kinds of decisions, and almost always it is the people in the producing countries.”

The terms of trade between many Third World producers and the First World have been getting worse over the past 10 years. Growers of coffee, the world’s second most valuable commodity after oil, saw prices crash to unprecedented lows in 2001. The International Coffee Agreement, which had helped to keep coffee prices stable by regulating supply through a Byzantine series of quota agreements, was abandoned in 1989, under pressure from First World countries urging the liberalisation of trade.

Since then, small producers have had to sell their beans immediately after they have been harvested, when prices tend to be lowest. Meanwhile, dealers on the London and New York commodity exchanges have been making millions on the fluctuations of the market while the big coffee brands in the First World have been paying less for their raw material.

At the same time, the World Bank has put many coffee-producing countries under pressure to disband national organisations that had acted as intermediaries between small farmers and the market. Subsidies were ruthlessly cut back and profit-motivated exporters took over the national markets. Many small farmers found themselves exposed to the chill blasts of the international coffee business just when it turned most unfriendly.

The consequences in coffee-producing countries such as Ethiopia have been disastrous. “As many people know, half the country is on its knees because of drought,” says Harriet Lamb. “Fewer people know that the other half of the country is on its knees because of the collapse in the coffee price. We found people who hadn’t bought clothes for four years, who were selling the roofs off their own houses; who were not having children because producing coffee does not sustain them any more.”

A similarly desperate situation has developed in most major commodity markets. A massive fall in the price of cocoa, for instance, has been one of the main reasons for the bloody civil war and an increase in the use of child slave labour in the Ivory Coast.

In the banana trade, the consequences of British people’s buying decisions were, until 1992, moderated by restrictive trade agreements between the British government and producers in the Windward Islands, where banana cultivation has traditionally been controlled by smaller-scale, less intensive farms than the big South American plantations. The advent of a more liberalised European Single Market in 1992 has led to an ever-increasing market share for the Central American plantations and the big three producers - through the American Government and the World Trade Organisation - are now pressing for Europe to remove all restrictions on the trade. It is a bleak picture: human exploiting human, often without knowing they are doing it. So Harriet Lamb’s bubbly optimism about the future of the consumer economy comes as a shock.

For more than a decade, her organisation - the Fairtrade Foundation - has been sowing the seeds for what she believes may become a revolution in Britain’s supermarkets. The foundation’s raison d’etre is the Fairtrade Mark - a label it awards to products that meet internationally recognised standards of fair trade. They can be made by anyone (there are about 100 Fairtrade products in shops at the moment), but they all must pay guaranteed fair prices to producers in the Third World. For small farmers, this means a steady basis on which to invest in the future. For workers on large plantations, such as those that dominate the tea and banana-growing industries, it means fair wages, proper working conditions and freedom to organise unions.

Seventeen similar fair-trade organisations have been established across North America, Europe and Asia. The movement, which traces its roots back to a request from Mexican farmers in 1986 for “fair trade not aid”, now has 350 producer groups in 36 countries selling to hundreds of registered importers, licensees and retailers.

What has surprised even the most enthusiastic fair traders is the recent growth in demand for their goods among mainstream consumers. Since 1994, when the British Fairtrade mark was launched, retail sales have risen to pound;62.6 million in 2002. They have more than doubled in the past three years, and Fairtrade produce now accounts for 14 per cent of the roast and ground coffee market. One and a half million Fairtrade bananas are eaten each week in Britain.

While some retailers still drag their feet, the past two years have seen a rush of big shops to the cause. The Co-op and Sainsbury’s - both leaders in the field - have started building their own brands of fair-trade products, while also carrying the wide range of branded Fairtrade goods sold by most of their competitors. The coffee-shop Starbucks now offers Fairtrade produce as an option, and the sandwich shop Pret a Manger is preparing to sell only Fairtrade coffee.

Harriet Lamb admits that fair-trade goods are often more expensive than non-fair-trade alternatives (for the obvious reason that they are not exploitative), but she points out that this is not always the case.

Sometimes the cut taken by producers can be such a small component of the price of non-fair-trade products that the consequences of increasing that share are trivial.

“Even if it does cost a bit extra, our experience is that people are shocked if you tell them that producers of the things they buy are doing so at prices below the costs of production,” says Harriet Lamb. “The public, if they are given the choice and the information, generally don’t want to exploit others.”

While the current range of goods with the Fairtrade mark in Britain is mainly confined to food products, such as tea, coffee, cocoa, chocolate, honey, sugar and fruit, the Foundation expects to give greater attention in the near future to clothing, especially cotton products. “The range of what we can offer is growing every year, and the demand is also growing very fast. We are on the brink of a really significant change in consuming habits,” she says. “There is a buzz throughout the Fairtrade movement - a feeling that an awful lot of people are starting to listen to us.”

For people such as Denise Sutherland, a member of Langley Park Fairtrade Group - a banana-growing co-operative on St Vincent in the Windward Islands - that interest from Western consumers means the difference between poverty and a decent standard of living. “First there were the chairs,” explains Denise, referring to chairs for the community hall bought by extra income from the Fairtrade premium. “Then there was a bridge, and a nebuliser at the clinic. We even have a computer now at the school.”

Her own home also shows the difference. “I was able to get the roof fixed after Hurricane Lilly,” she says. “And I’m hoping to get the ceiling repaired, too.”

* Your class could win a a box of Dubble Fairtrade chocolate. See page 27 of Friday magazine for details