Genetically modified (GM) crops will need monitoring for years if they are grown in the UK, British scientists say.
By Alex Kirby
BBC News Online environment correspondent
The warning comes from the Royal Society, the UK's national academy of science.
It says ministers have failed to act on advice they were given nearly five years ago about GM monitoring.
The society says they should not guess what will work and then simply hope for the best.
In a submission to the government's GM Science Review, the society urges the government to review its mechanisms for monitoring GM crops in the environment.
It also calls on ministers to produce plans for long-term assessments which must be taken into account by both UK and European Union regulators.
Filling the breach
Professor Patrick Bateson of the society said: "We advised the government almost five years ago that it needed to carry out a review of the way in which the environmental impact of GM crops is monitored in the long-term, but it still hasn't taken the necessary action.
"We are glad to see that the Advisory Committee on Releases to the Environment is now getting to grips with this issue.
"If the decision is taken to allow commercial planting of GM crops, it is essential that regulators in both the UK and EU monitor the environmental impact to pick up any potentially beneficial or harmful effects over a long period.
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"It will not be enough to make best estimates at the start and then assume that everything will turn out as expected."
The society also thinks the GM Science Review panel should be able to consider formally the results of the GM trials, the farm-scale evaluations.
It believes GM crops could confer worldwide benefits if they were used correctly.
Professor Bateson said: "There are many crucial decisions to be made concerning the use of GM crops... that will affect the future of humanity and the planet's natural resources.
"It is vital that these decisions are based on the best scientific information... GM technology may help to meet the demand for food by an expanding world population, with less impact on the environment.
"It is clear, however, that continued development and evaluations of GM technology will be required to realise these potential benefits."
A widespread public consultation on the issue is due to begin next month. Later this year the government will decide whether to license commercial GM crops.
This year will see fateful decisions
Tony Combes, on behalf of abc, the UK's Agricultural Biotechnology Council, an industry group, told BBC News Online: "The biotech industry spends millions of pounds ensuring environmental protection throughout decades of crop R&D.
"All GM products are subject to rigorous environmental safety assessment before they are placed on the market.
"Long-term general surveillance for unanticipated effects is an important aspect of current EU legislation, and industry is committed to work within these regulations.
"How else will the benefits experienced by six million farmers in 17 other countries be measured?"
Pete Riley, Friends of the Earth's GM campaigner, told BBC News Online: "If the Royal Society has concerns about the potential environmental impacts of GM crops it should oppose their commercial development.
"Long-term monitoring will not prevent damage that has already been caused. Biotech companies must not be allowed to turn our countryside into one huge outdoor experiment."
Images courtesy of Monsanto