Protesters have renewed their threat to sabotage a scientific site where a strain of genetically modified wheat is being tested outdoors.
Scientists from Rothamsted Research wrote an open letter this week appealing to the activists not to destroy "years of work" by attacking the test field in Harpenden, Hertfordshire.
Yesterday, the protest group Take the Flour Back invited the researchers to an "open exchange of opinions and concerns", but did not withdraw their threat.
The world's first GM wheat can repel insect pests, removing the need for pesticides. But activists claim outdoor testing could contaminate nearby fields.