The tests, conducted over the past three years, studied the risk of 'invasion' by oilseed rape if it carried extra, foreign genes. In a report published today, the researchers say that where they did see a difference, the engineered crops were less invasive and less persistent.
The scientists, from Imperial College, present their work in today's issue of the science journal Nature. In an accompanying article, Peter Kareiva, from the department of zoology at the University of Washington, predicts that the work will help to guide other scientists trying to assess the invasiveness of engineered plants.
But the pounds 1m study has been criticised by Mark Williamson, a member of the Government's Advisory Committee on Release to the Environment, which approved the trials. He said the experiments looked only at 'natural' habitats, not at the agricultural or semi-agricultural stretches that represent the majority of UK land cover.
This was where the biggest anxieties lay, since vegetable growers feared that plants such as those given genes making them resistant to herbicide might cross-pollinate with wild species and make these more difficult for farmers to eradicate. Professor Williamson said: 'The experiments asked 'is oilseed rape going to become a pest?' in habitats where we already know the answer is no.'
But Mick Crawley, who led the study, said the researchers created conditions in each of the habitats that were ideal for oilseed rape. 'We used disturbed ground, free from competitors.' The chosen spots, in Sutherland, Scotland, Bodmin, Cornwall and Ascot in Berkshire, included estuarine oak woodland, grassland, waste ground, bracken and peat bog. Professor Crawley said the engineered plants grew in all of the habitats.
Natural habitats were important because they went unnoticed by farmers. 'That's where problems begin and fester,' he said.
But he sounded his own note of caution: 'We must be super careful, however, not to extrapolate.' Other crops, engineered to be insect or drought resistant, would behave differently, he said.