Genes will inevitably escape from genetically modified crops, contaminating organic farms, creating superweeds, and driving wild plants to extinction, an official EU study concludes.
It adds that the three GM crops at present being trialled in Britain – maize, sugar beet and oilseed rape – pose the greatest risks of all the varieties it examined.
The study, just published by the European Environment Agency, confirms environmentalists' worst fears and will make it very difficult for the Government to approve the commercial planting of GM crops in Britain.
Ministers, who have consistently promised not to permit the crops if they are found to endanger the environment, will have to make a decision next year after the completion of three years of trials. But the trials are primarily designed to examine the use of pesticides on GM crops, not to look for escaping genes.
The study concludes that "gene flow can occur over long distances", and that some varieties of GM crops interbreed with others "at higher frequencies and at greater distances than previously thought".
Pollen from the crops, it concluded, travelled far further than the official "isolation distances" laid down to separate them from ordinary crops, to prevent interbreeding, making a mockery of safety precautions.
Cross-pollination by GM oilseed rape has been recorded about two and a half miles away from the crop, compared to an isolation distance of 600m. Research in Scotland has suggested that bees could carry the pollen at least six miles. The report concludes: "Under current farm practices, local contamination between crops is inevitable."
Environmentalists will see it as a vindication of their view that organic and non-GM crops will not be able to co-exist for long before being contaminated, denying shoppers a choice of food.
The report warns that "over time even small amounts of gene flow can have important effects on evolutionary change". It expects superweeds, resistant to herbicides, to become "common" if GM crops are grown, and warns organic farmers will find it hard to sell their produce once it has been infiltrated by GM genes. And it adds that the interbreeding could lead to natural wild relatives of the crops becoming extinct.
Peter Melchett, the policy director of the Soil Association, said: "The Government and GM industry seem to have picked three of the most contaminating crops to test in the UK. After this report, there should be no question of ministers considering, even for a moment, allowing them to be grown commercially."