Scientists are expected to issue a statement today after Britain’s first open-air trial of GM wheat was vandalised.

It follows a break-in at the Rothamsted Research centre in Hertfordshire during which an intruder is believed to have damaged the GM field trial on Sunday (20 May).

Researchers spent the rest of the day walking the 400-acre site and assessing how much of the crop  was harmed in the incident.

Police later confirmed they had arrested a 50-year-old man on suspicion of criminal damage.

The GM trial aims to see whether transgenic wheat can repel aphids in the field. Scientists hope the experiment will be able to continue.

A Rothamsted spokesman told Farmers Weekly he expected to issue a statement on Monday (21 May), once he had all the facts at his disposal.

The non-commercial trial – which could lead to reductions in pesticide use – is being sponsored by Biotechnology and Biological Sciences Research Council.

Details of the attack started to emerge in a series of tweets by Rothamsted scientist Toby Bruce, who is leading the transgenic wheat research project.

“Just heard there’s been an attack on our field trial, don’t know if crops were vandalised,” he wrote at 8.51am on Sunday morning. “Very sad.”

Dr Bruce initially suggested a single intruder had spread wheat seed on to three of the plots, without causing any apparent damage.

But he later added: “Oh dear, there’s more: Damage to plot 7 where he has cut off the tops of quite a few of the plants and collected the material.”

It is not known at this stage who was responsible for the attack. But anti-GM activists have been planning a “mass action” against the GM trial.

The “Take the Flour Back!” website urges opponents to GM crops to meet one week later at Rothamsted, on Sunday (27 May).

The website includes a map showing the location of the GM wheat trial. It adds: “Or take your own action in your own way, at your own time. Together we can stop this trial.”

Earlier, Rothamsted sicentists pleaded with anti-GM campaigners not to destroy the plots.

An online petition to muster support for the scientists was signed by more than 5,000 people, including the actor and broadcaster Stephen Fry.

But the protest group Take The Flour Back refused to back down, vowing to “decontaminate” the site unless the research was halted.