So widely are genetically modified crops now grown around the world, for use in animal feed and as processed food ingredients, that feed importers in Europe and Asia are finding it difficult to supply customers who want non-GM soya or maize.

"You have to pay 10-15 per cent more for non-GM corn - if you can get it at all," says Ross Korves, a leading US agricultural economist.

As world food prices surge and shortages loom, genetically modified crops look increasingly tempting as a way to raise agricultural yields without using more energy or chemicals. Even in Europe, where GM crops have faced the strongest public resistance, more politicians, experts and farmers' leaders are speaking out in their favour. Sir David King, the UK government's former chief scientist (pictured below), is one who says GM is the only technology available to solve the world food price crisis.

This week's statement on food security by leaders of the Group of Eight industrial nations acknowledged the potential of GM crops with a commitment to "promote science-based risk analysis including on the contribution of seed varieties developed through biotechnology".

But many consumer and environmental groups remain opposed to what some call Frankenfoods, saying they pose risks to human health and the environment. Critics say GM foods were not tested properly on animals before being put to commercial use in 1996 and some of the few tests produced troubling results, such as liver and kidney toxicity. GM supporters counter that any health effects would have become clear after a decade in which many millions of people have eaten biotech foods.

On the environment, opponents say GM crops reduce biodiversity and threaten wild plants and animals. Supporters say the environmental benefits, such as reduced pesticide spraying, outweigh any adverse effects.

In the Americas and parts of Asia, the area planted with GM crops has been growing fast for several years. According to the US-based International Service for the Acquisition of Agri-biotech Applications (Isaaa), which monitors GM globally, the world total grew by 12 per cent to 114m hectares in 2007.

Clive James, Isaaa chairman, predicts that GM planting will more than double over the next eight years, to cover 20 per cent of the world's farmland. He detects a big shift in mood this year. "The change has been driven by two concerns," he says. "One is the skyrocketing price of agricultural commodities and the other is better knowledge of what plant biotechnology can do to mitigate climate change."

Virtually all the planting so far has involved just four crops - soya beans, maize (corn), cotton and canola (oilseed rape) - and two traits: resistance to herbicide and insect pests. As GM opponents point out, these first-generation biotech crops do not increase yields directly. Grown in perfect conditions, they do no better than the same plant varieties without added genes. Instead, the point is to help farmers cope with weeds and insects.

Herbicide tolerance still dominates the GM market. The biggest brand is Monsanto's Round­up Ready. This enables the farmer to eliminate weeds by spraying with Roundup, an inexpensive broad-acting herbicide, without harming the crop.

The second trait in widespread use is insect resistance. A gene from a microbe called Bacillus thuringiensis (Bt) is transferred into the crop, which produces a toxin that kills voracious pests such as corn borers and bollworms. A study released last month by PG Economics, a UK-based agricultural consultancy, concludes: "Biotech crop commercialisation has resulted in significant global economic and environmental benefits and is making important contributions to global food security."

Graham Brookes, co-author of the report, adds: "Since 1996, biotech crop adoption has contributed to reducing the release of greenhouse gas emissions from agriculture, decreased pesticide spraying and significantly boosted farmers' incomes." Net economic benefits at the farm level amounted to $33.8bn (£17.1bn, €21.5bn) over 11 years, split about equally between increased crop yields and reduced input costs.

Despite the political and environmental opposition, Europe is not entirely a GM-free continent. Bt maize - the only GM crop with a commercial licence in the European Union - is grown in Spain (around 75,000 hectares) and on a smaller scale in France, Germany, Slovakia, the Czech Republic, Romania and Portugal. But Europe's GM acreage is just 0.1 per cent of the world total.

Many European farmers are angry they are missing out on benefits of GM available to north American counterparts, says Mick Willoughby, who farms in Yorkshire and is vice-president for Europe of the UK Country Land and Business Association. "As far as I can gather, the vast majority of European farmers are for biotech crops," he says. "It is more expensive to feed livestock [in Europe than in the US] because EU regulations mean a lack of GM crops."

Helen Ferrier, chief scientific adviser for the UK National Farmers Union, agrees. "European farmers should have the choice of using this technology if they wish," she says. "With high input prices and increasing global competition, the majority of our members would like to receive the benefits of GM crops." Ms Ferrier says the issue is not just that European farmers cannot use GM crops available today but that the agricultural biotechnology industry is concentrating its research and development effort on producing GM varieties for markets where they are likely to be accepted - and ignoring Europe.

While today's GM crops are designed to resist what scientists call "biotic stress" - pests and weeds - the second generation, currently under development, will focus on "abiotic stress". This encompasses non-biological factors such as drought and floods, heat and cold, salinity and acidity. The biggest research effort is to make plants use water more efficiently.

"Abiotic stress reduces yield in major crops by 65-80 per cent," says Michael Metzlaff, head of crop productivity for Bayer of Germany. His company's experiments show that "gene silencing" technology can reduce the production of a key enzyme called Parp, which controls plants' response to stress. As a result the plant grows better under adverse conditions. Companies plan to launch drought-resistant maize varieties between 2012 and 2015. Chris Zinselmeier, head of water optimisation research for Syngenta of Switzerland, says the aim is to produce a strain that yields better than conventional maize in drought years but "carries no yield penalty when water is plentiful".

In addition to drought resistance, the industry is working on several other traits. One product, Syngenta's Corn Amylase, shows how GM could help the biofuels industry. It is maize genetically modified to produce high levels of an enzyme, alpha amylase, that is a critical ingredient in the production of bio-ethanol. John Atkin, Syngenta's head of crop protection, says Corn Amylase will improve the efficiency of bio-ethanol manufacturing from maize by 5-10 per cent.

Monsanto is meanwhile working on adding genes that enable crops to use nitrogen more efficiently. Nitrogen fertilisers represent one of the largest input costs in agriculture: in the US alone, farmers spend more than $3bn a year applying nitrogen fertilisers to maize fields and at least half of the nitrogen is wasted because it is not taken up by the crop.

Colin Merritt, Monsanto's head of external affairs, says more efficient nitrogen use will reduce agriculture's contribution to global warming - currently estimated at 17 per cent of all human activity. In particular, it will cut emissions of nitrous oxide, a powerful greenhouse gas.

Monsanto has dominated agricultural biotechnology from the start and has always been the corporate symbol of GM food, for good and for evil. Last year the St Louis-based company was responsible for an estimated 100m hectares of the global total of 114m hectares sown with GM crops. Its sales of biotech seeds and technology reached $5.4bn in the nine months to May.

Although Monsanto was the main target of European opposition to GM in the 1990s - and is seen even by many GM supporters as having handled it badly - Europe had a strong research base in plant biotechnology at that time, both in companies such as Syngenta, Bayer and BASF and in universities and public research institutes. The anti-GM campaign was disastrous for European plant biotechnology, which has since been run down in both the public and private sectors. Even Syngenta, a merger between the agrichemical interests of Switzerland's Novartis and Britain's AstraZeneca, has shifted almost all of its GM research to the US.

Although Monsanto's corporate prospects look bright, its dominance is likely to fade as genetic engineering transforms other crops such as rice and wheat. Monsanto itself plans to concentrate on making further improvements to its four core crops (soya, maize, cotton and canola) and on producing GM vegetables, says Mr Merritt.

"The most important event in the next five years is the expected approval of biotech rice," says Isaaa's Mr James. Extensive field trials of Bt rice are taking place in China, India and other Asian countries. In addition, "golden rice", which has added genes to produce yellow beta-carotene in its grains, promises to relieve vitamin A deficiency in poor countries.

Farmers in the industrialised world are more interested in GM wheat, though this is unlikely to be commercially available for eight to 10 years. Its development has been delayed partly for technical reasons - the wheat genome is harder to manipulate than maize - and partly because Monsanto and other companies judged that consumer resistance would be particularly strong for a crop used to make bread.

All the talk of solving the world's food crisis through GM cuts little ice with committed environmental campaigners. "The government has been seriously misled if it thinks that GM crops are going to help tackle the food crisis - GM crops do not increase yields or tackle hunger and poverty," says Clare Oxborrow, UK food campaigner for Friends of the Earth. "Instead of helping the GM industry to use the food crisis for financial gain, the government should be encouraging a radical shift towards sustainable farming systems that genuinely benefit local farmers, communities and the environment worldwide."

GM proponents do not pretend that they can solve the world food problem. In the developing world, better soil management and improved infrastructure would do more than biotech crops to increase food supplies. But moves to supplement other measures with genetic engineering seem irresistible.

ANIMALS PROVIDE ONE GLOWING SUCCESS

Americans may have come to accept food from genetically modified plants but GM animals seem to be a step too far even for US consumer opinion.

Scientists first added genes from other species to farm animals in the mid-1980s, at about the same time as they began to make experimental GM crops. Technically there is no reason why the fields should not be alive by now with sheep and cows genetically engineered to resist diseases such as mastitis or produce leaner meat and more nutritious milk.

Yet while millions of GM mice are used every year in pharmaceutical and biomedical research, an adverse political and regulatory environment has inhibited most development and all commercialisation of GM farm animals.

Last month the US Biotechnology Industry Organizationissued a report enthusing about the potential of GM animals to "enhance human health, food production, environmental protection, animal health and cutting-edge industrial applications". Scott Gottlieb, the report's co-author, says: "The practical benefits of this technology have not yet reached patients and consumers primarily because of regulatory and political obstacles rather than the limits of science."

Dr Gottlieb, who was deputy commissioner at the US Food and Drug Administration from 2005 to 2007, was told when he left the FDA that a regulatory framework for GM animals - covering both food applications and the production of proteins to treat human disease - would be completed within a month. Yet nothing has appeared.

Altogether, "the FDA has spent 10 years on this", he says. "The agency has answered all the scientific questions - and gone back and answered them again. What has stymied it is the lack of political will. There is certainly a perception in government that this is not a winning issue."

Part of the problem is the "yuck factor" that many people feel when thinking about animal genetic engineering, Dr Gottlieb concedes. "Political leadership should have the courage to face the public on this."

The strength of the "yuck factor" was illustrated this year over another issue: the cloning of elite livestock. The FDA ruled that meat and milk from clones of cattle, pigs and goats and their offspring were as safe as from traditionally bred animals. But consumer groups urged a boycott and the US Department of Agriculture asked producers to maintain a moratorium on the sale of food from clones.

The only GM animals on the US market are not bred for food but for fun. Aquarium zebrafish, with added genes to make them fluorescent, are sold in red, green and orange under the GloFish brand. GloFish are banned in Europe and in the state of California. A GM fish that has been developed for food is the AquAdvantage salmon, engineered to grow three times faster and use feed more efficiently. Aqua Bounty, the Massachusetts-based developer, says it is on track for a commercial test in 2009.

The most advanced land animal project may be the Enviropig, developed at the University of Guelph in Canada. The GM hogs would reduce pollution by excreting 60 per cent less phosphorous.