Commercial planting will not be allowed until enough data have been gathered. The assurance, amounting to an indefinite moratorium, will go some way to meeting concerns of the Government's wildlife advisers, English Nature, that the countryside may be devastated by new weedkillers which most of the crops are being designed to accommodate.
English Nature and its sister agencies in Wales and Scotland have called for a three-to-five-year moratorium on commercial plantings until research on the new weedkillers, and the possible transpollination effect on wild plants of the GM crops, has been carried out. Tony Blair has publicly rejected the moratorium call.
Mr Meacher said yesterday: "We need the accurate, scientifically based data on which we can make the judgment that the sowing of GM crops and the use of their accompanying herbicides does not cause significant damage to the environment."
His comments came as the Government took the unprecedented step of issuing all its MPs with a "fact-pack" signed by five ministers and designed to quell fears over GM crops.
It illustrates the depth of government anxiety over the issue. "The Government recognises there is public concern about genetic modification. It is a fast-moving science and we accept we do not always have all the answers. We want to understand people's views," the letter said.
At present the Government has agreed a voluntary moratorium on commercial GM plantings with the biotechnology industry until spring 2000. Yesterday both English Nature and the Royal Society for the Protection of Birds said that that this would not nearly be long enough for proper test data to be gathered.
Two farms are being used this summer to test the large-scale environmental effects of growing oilseed rape genetically modified to be herbicide-tolerant, which is first in the queue for commercial growth in the UK.
But Mr Meacher said that if not enough data had been collected by next spring, he would go back to the biotechnology companies and explain that more time was needed.
In the light of current publicity, he said, he would expect them to co- operate, but hinted that if they did not, the Government would force them to.
Although Monsanto and Zeneca, two of the biggest biotechnology companies, said on Wednesday that they would fight, in the European Court, any enforced delay on commercial plantings, Article 16 of the European Union directive regulating GM crop plantings gives the Government power to stop them and revoke licences already given, if new information is discovered that they may be harmful to the environment.