The map of genetically modified Britain: 80 farms sowing the seeds of controversy

Large-scale trials of genetically modified crops are to go ahead soon at up to 80 farms in England and Scotland, the Government said yesterday, setting itself on a collision course with environmental groups.

The trials - to gauge the effects on wildlife of the new, more deadly weedkillers GM crops are designed to tolerate - will involve oil seed rape, maize and beet. They will last three years, Michael Meacher, the Environment minister, announced. Biotech companies have agreed a moratorium on growing GM crops commercially in Britain until the results of the trials are available.

Mr Meacher released the exact locations of the first 30 trial sites and promised to reveal the rest, despite the fact that several GM crop fields in last year's trials pilot programme were attacked by activists. After one incident in Norfolk, Lord Melchett, executive director of Greenpeace, was charged. He is awaiting trial with other members.

Mr Meacher gave not only the names of the nearest villages, but also six-figure grid references, making it possible to identify individual trial fields. "I know this is greatly resisted in some quarters, but I am extremely keen this should remain as open and transparent an exercise as we can make it," he said. No special protection from police or security guards had been lined up for the farms concerned, Mr Meacher said. "The police will, of course, provide what security they reasonably can."

The minister said anyone contemplating illegal actionshould remember that the purpose of the trials was to gather information that might lead to GM crops being banned in Britain as harmful to wildlife. "To try to block them... is in my view simply shooting themselves in the foot."

The trials are supported by the Royal Society for the Protection of Birds and by English Nature, the Government's conservation advisers.

However, the Soil Association, the lobby group for the organic food movement, said it was outraged. "We are really despondent that the Government continues to take into account industry's demands to grow GM crops in the environment before adequate safety tests have been done," said Harry Hadaway, the association's GM campaign officer.

Mr Meacher said potential pollen transfer from the GM crops to nearby fields would be monitored in the trials, but the Soil Association says the quarantine distances proposed are quite inadequate. The maximum safety distance from organic crops suggested in the trial guidelines is 600 metres, while the Soil Association carries out a detailed risk assessment of any organic farm within six miles of a GM site. At least 30 organic farms are within six miles of the GM sites and at least one is within a mile, Mr Hadaway said.

The trials are also bitterly opposed by more radical groups such Greenpeace and Friends of the Earth. "The Government is gambling with the future of the British countryside," said Pete Riley, Friends of the Earth's food campaigner.

Lord Melchett accused the Government of "genetic tyranny". He said: "Britain will be bombarded with GM pollen with no regard for wildlife, the public or GM-free farmers."

Friends of the Earth said it would not attack sites - "there are other means of stopping this scientifically nonsensical programme" - but Greenpeace said it had made no decision.Smaller, less mainstreamgroups may well take direct action.

Aware of the potential for local and pressure group opposition, the Government is organising at least a dozen public meetings near the main sites. The trials, involving up to 25 fields each for spring-sown oil seed rape and maize, and 30 fields in total for sugar beet and forage beet, have nothing to do with food safety. The focus is on how growing the crops affects flowers, insects and birds.

The rape and maize have been genetically engineered by the biotech company Aventis (formerly AgrEvo) to be tolerant of its weedkiller glufosinate ammonium (trade name Liberty), while the beet has been engineered by Monsanto to tolerate its herbicide glyphosate, commercially known as Roundup.

Both are "broad spectrum" herbicides,much more powerful than conventional weedkillers. Yet it is on other weeds and wildflowers that wildlife in the fields depends.

The companies say less of the new herbicides is needed than conventional weedkillers, but conservationists say although the dosage may be less, the impact is far greater.

The first fields will be planted on about 30 March and the last fields in May, Mr Meacher said.

Dr Roger Turner, chairman of the umbrella body for the biotech and seed companies, SCIMAC (the Supply Chain Initiative on Modified Agricultural Crops), said: "We are delighted that the Scientific Steering Committee has endorsed the programme for this year. Now we can get on with the job of answering the specific questions raised about GM crops on the basis of sound scientific evidence, not scaremongering and hysteria."