GM crops have often been targeted by protesters
Four anti-GM protesters who shackled themselves to tractors during a crop trial should have been convicted, the director of public prosecutions has said.
At a High Court hearing, the DPP asked for an earlier decision to acquit the activists of trespass to be reversed.
Elizabeth Snook, Olaf Bayer, Richard Whistance and William Hart were protesting against an experimental trial involving GM maize on farmland in Dorset.
But the DPP said Judge Roger House erred in law when he failed to convict them at Sherborne Magistrates' Court in March.
The protesters argued that they had been protecting the environment.
"The sewing of GM seeds in government trials was not criminal but sanctioned by law and they should have been convicted"
Director of Public Prosecutions
Miss Snook, 26, - who has previous convictions for similar acts of protest - told the Sherborne court that GM crops posed a "serious threat" to the eco-system, adding that their actions were carried out "as a last resort."
They were protesting against the trial of a pesticide-resistant GM-maize called "T-25" at the Horselynch Plantation at Littlemore, near Weymouth, Dorset on 16 May, 2002.
The magistrates court heard they had disrupted the start of the trial by locking themselves to tractors preparing to sew the seeds.
Judge Roger House ruled the four had acted in a "reasonable" way.
"I can see you all have huge knowledge of GM crops and I can see you were acting to protect the land and animals," he told them.
But Francis Chamberlain, appearing for the DPP, told Lord Justice Brooke sitting with Mr Justice Silber at the High Court, that there was no acceptable defence to the charges.
"The sewing of GM seeds in government trials was not criminal but sanctioned by law and they should have been convicted," he said.
The judges reserved their judgment until a later date.