Organic farming is a slow-to-grow, low-yield industry favoured by middle-class parents who have the time and money to meander the overpriced aisles of Waitrose, deliberating over wild rocket or white asparagus. Right?

Wrong, says Tewolde Berhan. He thinks organic farming could be the solution to Ethiopia's famines. The chief of the country's Environment Agency has worked his way through academia and government to become one of the world's most influential voices in the biotechnology field. Berhan believes that, properly applied, his approach could save the lives of many of the thousands of Africans who die every day as a result of hunger and poverty.

He maintains that genetically modified organisms (GMOs) remove control from local farmers. He speaks for a growing number who believe that Africa should return to natural, sustainable methods of agriculture better suited to its people and environment.

Can one man hope to stand against governments and the huge multinationals? Visiting London, Berhan appears to be a frail - if nattily dressed - sexagenarian. But our conversation reveals his determination, intelligence and encyclopedic memory, combining to create an indomitable force.

Asked why bad harvests seem to have a greater impact on Ethiopia than its neighbours, he has a simple yet stark response. "It's largely because of the lack of infrastructure," he says. "The road system in Ethiopia has doubled in the past 10 years, but is still very poor.

"Ethiopia is still an agrarian society, and there isn't one such country that hasn't had famines," he adds. "The reasons are clear: some years you have plenty and others not enough. If you don't have the technological and financial capacity and the infrastructure to store in good years, you can't make provision for the bad. People here depend entirely on the crops they produce in their fields, so when one season fails, the result is famine."

Born in 1940, Berhan graduated in 1963 from Addis Ababa University and took a doctorate at the University of Wales in 1969. Later posts as dean of science at Addis Ababa, keeper of the National Herbarium and director of the Ethiopian Conservation Strategy Secretariat kept him in touch with the agricultural needs of Ethiopia's people.

In 1995, he was made director general of the Environmental Protection Authority of Ethiopia, in effect becoming the country's chief scientist in agriculture. A strong critic of GMOs, he's a powerful voice in lobbying on food safety. His most notable triumph came in negotiations on biosafety in Cartagena, Colombia in 1999. Berhan acted as chief negotiator for a group of southern hemisphere countries. He helped to secure an agreement to protect biosafety and biodiversity, while maintaining respect for the traditional rights of the Third World population, gained against strong opposition from the European Union and North America.

So why is organic farming the answer? Given low yields, poor soil and drought, you'd think that industrial farming would help Ethiopia to maximise production. Not so, Berhan says. "Organic farming deviates little from the natural environment in supplying nutrients to crops. We've developed the ability to change things in a big way and, without considering the consequences, we create disasters. Look at what happened with DDT.

"Organic farming disturbs nature as little as possible and reduces those risks. Intensive farming has led to the exacerbation of pests and diseases, and loss of flavour in food."

These views are at odds with the "conventional" industry. Tony Combes, the director of corporate affairs for Monsanto UK, a big player in the GM market, says: "Going organic isn't the way to increase yields. But then, neither is going totally GM. Farmers need solutions suitable for local predicaments. This means choosing from a range of options - organic, conventional and GM. If yields can be increased, that surplus can be sold."

Berhan is undeterred. He has persuaded the Ethiopian government to let him demonstrate his ideas in the Axum area of Ethiopia. Old field-management techniques have been resurrected, while methods new to the area, like compost-making, have been successful.

Those who think organic farming means low yields will be surprised by Berhan's evidence. "When well managed, and as fertility builds over years, organic agriculture isn't inferior in yield. Now, farmers don't want chemical fertilisers. They say, 'Why should we pay for something we can get for free?'"

Berhan expresses gratitude for the West's famine-relief efforts, but he has reservations. "When countries want to help, they may not know how, so the intention has to be appreciated. But if you go beyond the intention and begin to dictate terms, it becomes more sinister. In times of shortage, making food aid available is helpful - for that year. If you keep making it available, you discourage production."

He believes there are times when food aid can be more about control by Western governments than assistance. "The feeling is strong that this is deliberate. I attended a meeting where farmers from the USA were present. I told them a story I'd read about how rice production in Liberia was depressed because of cheap imports from the USA. The American farmers said this was a deliberate policy by the US State Department to make countries dependent on them for food.

"I began to investigate and discovered that, while the EU has abandoned its policy of providing food aid, initially sending money so that food can be bought locally, the US still insists it will only give food in kind. This makes me feel those farmers were right."

Berhan insists on the necessity of further trials for GM crops, and believes extreme caution should be used in their growth and trade. His application for a visa to attend talks in Canada on GM labelling was turned down earlier this year, suggesting that his influence is feared. "We were finalising the labelling of grain commodities," he says. "A compromise had been reached in 2000 for labelling to say, 'This product may contain GMOs,' but we wanted to toughen it up, to say, 'This product contains these GMOs,' and to list them."

He also contests that GMOs give higher yield. "This is mainly hype. So far, there's not one GM crop that produces higher yields per acre than conventional crops. They offer an economical advantage to farmers as they can apply herbicide in large doses and not have to worry about weeds: that's all."

After protests from the media and groups such as Greenpeace, the visa was granted. Dr Eric Darier, GM campaigner for Greenpeace Canada, explained why it was so important that Berhan attended. "He is truly one of the key 'fathers' of the biosafety protocol," Darier says. "It was convenient for the Canadian government [to refuse the visa], as it prevented a major critic and opponent of pro-GM Canadian policy from attending two of the three days of the workshop on liability. Canada has failed to ratify the biosafety protocol. In view of the fact that the Canadian government has done everything to undermine the efforts of the international community to adopt a strict, effective biosafety protocol, the delays in issuing the visa are evidence of Canada's bad faith."

Is Berhan bitter? Far from it. "I think [the visa refusal] was based on a mistaken calculation. If anything, it gave the labelling issue higher visibility. We told the Canadian government: either you accept multilateral discussions, or the Office for the Commission of Biological Diversity [based in Montreal], must move to another country." The threat worked.

Berhan's message is compelling - and he is in demand worldwide. In the past month alone, he has travelled to Austria, the UK, Tunisia and Norway. He returns to the UK in July to give a talk for the Soil Association, where he will ask: "Can Organic Farming Feed the World?" He is a huge force in trying to prove that it can.

The Soil Association will be at the Royal Geographical Society in London on Tuesday 12 July (0117 987 4586; www.soilassociation.org )