Since 1998, researchers backed by the government's Scientific Steering Committee have been evaluating the impact of GM herbicides on the local environment and comparing the results with studies on nearby fields where conventional weed killers were used on non-GM varieties.

Although the results remain a closely guarded secret, many observers are expecting a largely mixed verdict on Thursday, most likely pointing out that in trials of GM rapeseed and sugar beet varieties, insect and weed numbers fell, while those in GM maize fields were much less affected.

The trials, which tested GM rapeseed and maize produced by Bayer CropScience, the UK arm of German biotech giant Bayer AG, and sugar beet made by U.S. agrochemicals producer Monsanto, did not investigate whether conventional or organic crops could co-exist safely alongside GM crops.

A full report by the government's Agriculture and Environment Biotechnology Commission (AEBC) is expected to report on this, and the question of liability, later this month.

But research papers published by Britain's Department of Environment, Food and Rural Development (DEFRA) earlier this week failed to show GM crops in a positive light.

In two separate studies, researchers found that bees carrying GM rapeseed pollen had contaminated conventional plants more than 16 miles away and that if farmers grew GM rapeseed for one season, impurities could stay in the soil for up to 16 years if not "rigorously controlled."

Once published, Thursday's trial results will immediately be forwarded to ACRE, the government's statutory advisory body on the release of GMO, which will advise the government on the implications of the results for any existing or pending or future releases of GM crops.

But before ACRE members formulate their advice, they will be holding two open meetings, to be held in London and Edinburgh on November 25 and December 4, respectively.

A government decision could come later this year, or early in 2004.

There are no GM crops in the ground in the UK at present and no imminent plantings.

Led by the United States, GM crops are now grown in more than 16 countries outside Europe.