Campaigners against genetically modified crops have slammed the government's consultation with the public.

Launched on Tuesday, "GM Nation?" involves six regional debates in Birmingham, Swansea, Taunton, Belfast, Glasgow and Harrogate, along with a series of discussions held by county councils.

Although the debates will run for six weeks until mid-July, results of four-year crop trials are not expected until September.

Environmental campaigners and consumer rights groups united on the first day claiming the exercise was a sham.

Shadow secretary of state for trade and industry, Tim Yeo, challenged the way ministers had organised the exercise.

"The start of the much vaunted debate about genetic modification has been a fiasco, increasing rather than diminishing public confidence about the issue. Matters have been made worse by the government's blurring of the consumer, health and environmental aspects," he said.

"The government must commit to accepting independent scientific advice as the basis for deciding Britain's approach to this technology and to putting protection of the consumer at the heart of this approach."

The Liberal Democrats called on the government to rethink the consultation and include the results of the farm-scale trials.

"The government's public consultation on GM food is little more than window dressing," said food and rural affairs spokesman Andrew George.

"There are serious doubts as to whether the consultation will influence the decision on the commercialisation of GM crops. The consensus from consumer and environmental groups, criticising the purpose, parameters and timing of the debate, should be heeded by the government."

An alliance of eight associations, including the RSPB and the National Trust wrote to environment secretary Margaret Beckett expressing their concerns and calling for the debate period to be extended until October, with publication of the final report delayed until early in 2004.

Among their concerns are a shortage of local meetings, basic materials to facilitate the debates and a lack of information concerning how public opinions will feed into the final decision.

"We appreciate that the government wants a resolution to the issue, but we believe that a proper process would be in the public interest," the letter said.

"A better process would allow the farm scale evaluation results to be considered during the debate rather than being published once it has ended."

The Consumers' Association was one of the groups behind the letter.

"The organisation of the GM public debate can only be described as a catalogue of errors from start to finish with the government paying mere lip service to consumer concerns," said director Sheila McKechnie.

"Enough is enough. Consumers deserve a genuine chance to have their views heard and it is the responsibility of Margaret Beckett's department to make sure that they get it."

The Unison trade union and Greenpeace were also among the eight signatories, along with Friends of the Earth.

"The public has been making its feelings known on GM for the last six years, but the government has not been willing to listen," said FotE policy and campaigns director, Liana Stupples.

"Now that they are finally inviting people to express their concerns, the government must take this debate seriously and show that they are doing so."

However, the independent steering group running the debates has defended the organisation.

"We're providing a toolkit for debates at every kind of level - a film, a CD-Rom, an interactive website, a booklet of background material and a team of facilitators on demand for larger meetings," said GM Nation? chairman Professor Malcolm Grant.