Two of the three Genetically Modified (GM) crops grown experimentally in Britain, oil seed rape and sugar beet, appear more harmful to the environment than conventional crops and should not be grown in the UK, according to British scientists. They conclude that growing these crops is damaging to plant and insect life. The third crop, GM maize, allows the survival of more weeds and insects and might be recommended for approval, though some scientists still have reservations.

The results of the three years of field scale trials ? the largest scientific experiment of its type on GM crops undertaken anywhere in the world ? will be published next Friday by the august Philosophical Transactions of the Royal Society. The results have been closely guarded secret for months, and will be studied by scientists, farmers, food companies and governments across the world. The study will include eight peer-reviewed papers about the effect of growing GM crops and accompanying herbicides on the plants and animals living in the fields around. The paprs compare the GM fields with conventional crops grown in adjacent fields.

The overwhelming public hostility in the UK to GM crops has not been shared by scientists or the government but the results of the field scale trials are expected to be a jolt to the enthusiasts. The Royal Society refused to publish a ninth paper produced by the scientific group. The Society?s explanation was that the ninth paper was not a scientific document but a summary of findings and in effect a recommendation to the advisory committee on releases to the environment - the expert quango. The scientists involved will now themselves publish this summary at the same time as the other eight papers, concluding that two of the three crops should not be grown.

The trials were set up four years ago by the former environment minister, Michael Meacher, urged on by English Nature, the government?s watchdog on the natural world, which feared that the UK?s already declining farmland species might be further damaged by the introduction of GM crops.

A three-year moratorium on the commercial introduction of crops was negotiated with the GM companies Monsanto, Syngenta and Bayer Bioscience while the experimental field trials took place. Despite repeated attacks by anti-GM protesters that destroyed many of the fields, the scientists decided they had enough results to be scientifically valid. Experts not involved in the trials had not expected definitive results even though hundreds of fields were used.

The numbers of weed species and various types of spiders, ground beetles, butterflies, moths and bees in fields of GM crops and the adjacent conventional crop fields were counted to see if they showed marked differences. All were treated with herbicides to kill weeds but the GM crops were modified to survive special types made by Monsanto and Bayer.

The papers accepted for publication by the Royal Society show that in GM sugar beet and oil seed rape the weeds and insects were significantly less numerous. Spraying with the Monsanto herbicide glyphosate had taken a heavy toll in the beet fields and the Bayer product glufosinate ammonium had wiped out many species in the rape fields.

For maize the reverse appears to be the case. The reason seems to be that maize fields are normally sprayed with atrazine, which kills weeds as they germinate, and is an even more savage killer than the Bayer product. But the result may be controversial because maize is particularly sensitive to competition from weeds and yields may be down. Farmers in America found glufosinate ammonium was not enough to kill competitive weeds and used a second herbicide, further damaging biodiversity.