The government has given details of the 28 sites in England and Wales where trials of genetically modified (GM) maize will take place. Weather and soil conditions permitting the maize will be sown from the end of April and through May.

Four more maize sites may be decided upon in the near future to meet the target of 32 sites requested by the scientific steering committee which oversees the farm-scale evaluation programme.

In Wales, where assembly members have already expressed a desire to avoid GM crop trials, the announcement has provoked anger at the way in which the Department of the Environment, Transport and the Regions has made its decisions.

Assembly minister for rural affairs Carwyn Jones has expressed his worries over the announcement that two test sites will be in Pembrokeshire and one in Flintshire.

Jones said: "My concerns relate to the potential for cross-pollination of neighbouring crops, particularly those in organic production, and uncertainty over the issue of liability for economic loss incurred."

Nick Bourne, the leader of the Welsh Conservatives, said that the trials "could spell yet further disaster" for Wales and warned of the dangers of cross-pollination.

"I am absolutely furious at the way in which Westminster, fully knowing of the assembly's stance on GM testing, has decided to completely ignore thewishes of the people of Wales and push ahead with a GM testing programme," said Bourne.

Plaid Cymru have supported the application of the "precautionary principle" to the GM trials and said the issue provided a good example of why the Welsh assembly needed more powers.

Plaid Cymru MP Simon Thomas called the announcement "insensitive and crass" and said the assembly had been "simply ignored".

Carol Kearney of Friends of the Earth called the government's support for the biotech industry "staggering".

"Elections are delayed, footpaths are closed but trials of GM crops in infected foot and mouth areas are allowed to continue, despite the obvious risk they pose. If the prime minister is serious about agricultural sustainability he should cancel this year's trials and review the role of these crops in the long-term future of farming," she said.

The trials are designed to provide evidence on whether planting herbicide-tolerant GM crops and using weed killers associated with them will affect the diversity of wildlife. The evidence will be studied by the independent steering committee and the results made public at the end of the trials.