The Ministry of Agriculture, Fisheries and Food will publish a long-awaited report that will produce evidence of "transgenic pollution" from GM crops to neighbouring fields. The report, commissioned by Maff from the highly respected John Innes Centre, represents the most convincing research to date that seeds from modified plants can cross-pollinate.
Organic farmers have complained bitterly that their crops are at risk of contamination from pollen carried by the wind or by bees.
Ministers will announce an overhaul of guidelines issued to the biotechnology industry on safe planting distances from GM crops.
The Government will have "no option" but to increase the distances, currently set at 200 metres, ministerial sources have told The Independent.
Maff will invite organic groups and environmentalists, as well as biotech firms involved in farm-scale trials across the country, into talks to reset the guidelines in the light of the research.
The farm-scale plantings are covered by voluntary guidelines issued by the Supply Chain Initiative on Modified Agricultural Crops (Scimac), a body that regulates the industry.
Pressure on the Government will increase this week when the Soil Association issues strict new guidelines on planting distances to its own organic farmers. The Association will tell its members that it intends to withdraw its certification if regular checks on crops find evidence of cross- contamination.
Patrick Holden, director of the Soil Association, gave a cautious welcome last night to the suggestion that ministers were preparing to revise the guidelines. "We are pleased that the Government is prepared to have an open mind. If they want to increase the distances, we are very happy to talk to them," he said. "It's not too late to stop genetic pollution, but the Government has so far shown a massive abdication of responsibility on the issue and left us to police this. That has to change."
One organic farmer who had taken part in the farm-scale GM trials decided to burn the crops after the Soil Association threatened to withdraw certification. His organic beans had been just six metres away from GM crops.
The Government was yesterday forced on to the defensive when it emerged that there had been more than 100 meetings between ministries and biotech firms since it took power in 1997.
The John Innes Centre in Norwich is Europe's leading academic establishment examining GM foods. Its report accepts the premise that pollen from GM crops will be spread long distances by the wind and insects. Its results represent the first official backing for an earlier study by the National Pollen Research Unit on the threat of GM pollen and seeds contaminating organic farms many miles away.
Research by the Soil Association earlier this year showed that more than 80 per cent of rape seed pollen is carried by bees and bees can travel more than three miles. Wind can transport it by much further.
Both Michael Meacher, the Environment minister, and Elliot Morley, the Countryside minister, are understood to be in favour of giving greater support to organic farmers.
Tony Blair has repeatedly warned against "media hysteria" over the issue, but ministers unveiled new advisory bodies on GM last month in an attempt to calm public fears about the technology.
The Government will rule out as impractical calls for a six-mile "buffer zone" around every GM trial, but the organic lobby insists that it wants the Department for the Environment, Transport and the Regions to warn all organic farmers within the distance before any licence for trials is granted.
The John Innes report is understood to have found that one per cent of organic plants in any field could become GM hybrids because of the pollen spread. It concludes that contamination by either seed or pollen cannot be "entirely eliminated".
The Soil Association's tough certification procedures mean that scores of farmers could be put out of business if they fail to clear themselves as GM-free.
One senior government adviser said last night: "If this research shows that there is a risk, then ministers will have to respond positively to it."