GM crop campaigners in legal threat over plan for new trials.
Environmental activists Greenpeace accused the Government of flouting its own planning laws by authorising the planting of GM oilseed rape in 25 fields across the country, including three in Warwickshire, one in Worcestershire and one in Gloucestershire.
The organisation said it had taken legal advice and believed permission was needed for change of use as the fields were now being employed for research rather than agriculture.
It has written to Deputy Prime Minister Mr John Prescott and Agriculture Minister Mr Nick Brown demanding they seek planning permission or provide adequate reasons for their failure to do so.
A Greenpeace spokesman said: 'The Government's breathtaking arrogance in ignoring the rejection of GM technology by citizens and consumers - as well as the risk of genetic contamination - borders on the criminal.'
GM crops are already being planted at 49 farms across the country as part of a three-year project. Greenpeace and fellow campaigners Friends of the Earth have condemned the new trials, which will be held this autumn.
They said it was irresponsible for more trials to be held before it had been proved there was no genetic fall-out leading to cross-pollination of neighbouring plants.
Both groups warned anger among local people had led to crops being ruined in the past.