The report, compiled by the bio-technology unit of the Department of Transport Environment and the Regions, was intended for publication after it had been seen by scientists at its draft stage last summer.
But the report, Genetically Modified Crops: Wider Issues - Biodiversity In The Agricultural Environment, was shelved indefinitely after the Ministry of Agriculture Fisheries and Food objected on the grounds that it undermined current Government policy on GM crops.
It is understood that Jack Cunningham, chairman of the Cabinet committee on GM crops, backed MAFF and backed the decision to delay.
The study, leaked by Friends of the Earth, called the current regulatory framework "inadequate" and warned that the long-term effects of GM crops on biodiversity in the British countryside were "unknown".
The report says there would be "...a danger in overstating the benefits without explaining the risks".
The impact of GM crops resistant to pests could have important ramifications on the wildlife that depends on them, it said. Those species at risk include farmland birds such as the corn bunting, the grey partridge and the skylark. This would undermine Government own targets in restoring the population of the declining skylark.
Last night Friends of the Earth said the report now drove a "wedge" through the recent Downing Street attempts to present a united front on GM crops and foods.
Friends of the Earth spokesman Tony Juniper said: "It is very substantially supporting the view of English Nature about the impacts of GM crops on biodiversity, crops and their management and the effects on British wildlife.
"It drives a wedge into the heart of Government policy at a time when they are trying to marshal public opinion to support the whole idea of GM crops, their use and their use in our food."
t The Government's chief scientific adviser, Sir Robert May, said yesterday that there was "not much of a case" for retaining the beef-on-the-bone ban. He claimed it was politics rather than hard evidence that had kept the ban in place.Reuse content