Vital tests, which the Government planned to use to justify the planting of genetically modified maize in Britain, have been invalidated, The Independent on Sunday can reveal.
Michael Meacher - who as environment minister set up the trials, the results of which are due to be published on Thursday - said yesterday that the three-year tests will have to be done all over again, and that until then the Government "could not responsibly license GM crops".
The tests have been rendered invalid by a new European Union ban on a toxic weedkiller called atrazine, which is used on maize but is suspected of causing cancer and "gender-bender" effects. The use of the chemical - which was employed in the tests - is central to the Government's case that growing modified maize is relatively benign to the environment.
The ban - which could not have come at a more embarrassing moment for Tony Blair and his ministers - appears to knock away the last prop of their strategy to introduce GM crops to Britain, crowning a summer of setbacks. In July two reports by the Prime Minister's own officials and advisers, which had been expected enthusiastically to endorse the technology, instead urged caution. And last month a public consultation recorded majorities of nine to one against GM foods and crops.
The EU's move is crucial because the trials specifically concentrated on the effects of using different herbicides on GM and conventional crops. In a manoeuvre which environmentalists suspect was designed to make the tests as easy for the new technology as possible, they did not focus on the main threat: that genes from the modified plants would escape, creating superweeds and contaminating ordinary crops nearby.
However, leaks of the trial results suggest, as first reported by The Independent in the summer, that the herbicides used on two of the three planned GM crops - sugar beet and oilseed rape - damage wildlife and nearby plants more than those used on conventional ones. Growing of GM maize, by contrast, appears to have be found to be less damaging than normal farming of the cereal. Ministers have therefore been preparing to give it the green light, while banning GM oilseed rape, and postponing the introduction of GM sugar beet.
But the GM maize only appeared to perform well because the herbicide used on the conventional crop was the particularly hazardous atrazine. Last week it was banned by the EU under its Plant Protection Products Directive.
The Department of Environment admitted late last week that the ban meant atrazine would have to be phased out in Britain within 12 months: this means it would probably be withdrawn from use before GM maize was grown commercially,
Last night Mr Meacher said; "The ban on atrazine means that the trials are no longer valid because they no longer make a true comparison between the herbicides that would be used on GM and conventional maize. Clearly we have now got to have further trials, using the weedkillers that are actually going to be used. I do not see how the Government can now responsibly license GM crops."
Ministers will still be under pressure to try to find some way of giving the green light to the technology. But the invalidation of the tests and the outcome of the reports and public consultation means environmentalists would almost certainly challenge any such decision in the courts.