The long argument over whether or not genetically-modified crops should be commercially grown in Britain ended yesterday when the Environment Secretary, Margaret Beckett, announced a formal but heavily-qualified go-ahead for the growing of GM maize.

Her decision was denounced by environmental and consumer groups who have long contended that GM crops may damage the environment and are not wanted by the public.

But it was welcomed by the biotech industry, and by many leading scientists who insist that GM technology can bring many benefits to agriculture in the future.

Mrs Beckett based the Government's decision squarely on its own four-year-long, large-scale trial of three GM crops proposed for growth in Britain, all genetically-modified to be herbicide-tolerant to allow the use of extra-powerful weedkillers. Reporting last autumn, the trials found that in the case of beet and oilseed rape, the GM crops and their associated weedkillers were more likely to harm farmland wildlife such as insects, wild flowers and birds than their conventional crop equivalents. But with maize the opposite was true, and the GM crop was less damaging. On this basis, Mrs Beckett told MPs yesterday, the Government would oppose the cultivation of the particular varieties of GM beet and oilseed rape throughout the European Union but would agree "in principle" to the growing of GM maize.

She said GM growers would be expected to monitor changes in herbicide use on conventional maize. A much-raised objection to GM maize "passing its test" in the trials is that the weedkiller used with the conventional crops for comparison, atrazine, is such a deadly chemical that it is being phased out across Europe, and therefore the comparison was invalid.

Mrs Beckett indicated that the GM maize and other crops would only be grown under a legal liability regime by which organic farmers could seek damages if their own crops were contaminated with GM pollen, and that would have to be funded "by the GM sector itself, rather than by Government or producers of non- GM crops". Mrs Beckett said the Government intended to look at all applications to grow GM crops case by case.

The shadow agriculture minister, John Whittingdale, warned that despite the Government's decision, more than 40 regions in Britain wanted to declare themselves GM-free, including Cornwall, Devon, Somerset and the Lake District. He added that 90 per cent of the public had voiced opposition to the technology when they were questioned as part of last summer's GM debate.

Tony Juniper, director of Friends of the Earth, said the Government "has given the thumbs-up to GM maize and shown two fingers to the British".

But Professor Chris Lamb, director of a plant research establishment, the John Innes Centre in Norwich, said: "The lesson we must learn from GM is that if society is to reap the benefits that plant science can bring, we need long-term policy-making that identifies what it is society requires from agriculture and new plant-based industries."