BBC Political Editor Robin Oakley: "The government are having to rethink their stance on GM foods"

In the first case of its kind in this country, the American chemical giant, Monsanto, and the Worcestershire-based company, Perryfields, pleaded guilty before magistrates at Caistor in Lincolnshire.

The Health and Safety Executive brought the prosecution after a routine inspection of an experimental field of oil-seed rape last summer.

Monsanto failed to comply with the law covering the release of GM crops.

Investigators claim they found a barrier,designed to stop the transfer of GM pollen from herbicide-tolerant oilseed rape to neighbouring crops of un-modified oilseed, had been partially removed before flowering.

This, it is claimed, could lead to the cross-pollenation of the two.

Crown court call

Monsanto had said before the trial it would not be contesting the allegations in court. It was fined £17,000 and ordered to pay £6,159 court costs.

Tim Hirsch reports on the problem of cross pollination

Perryfields Holdings was fined £14,000 and ordered to pay £5,000 court costs.

Friends of the Earth had called for the case to be sent to crown court where penalties are heavier. Magistrates can impose a fine of up to £20,000, but crown court fines are unlimited.

BBC Science Correspondent Pallab Ghosh looks at the argument for and against GM foods

Friends of the Earth senior food campaigner Pete Riley described the fine as "pathetic" and said it should have been much heavier.

"To a company as large as Monsanto, it is less a slap on the wrist than a tickle with a legal feather," he said.

"The big biotech companies must stop playing Russian roulette with the British countryside."

Barrier 'mown down'

Dr Colin Merritt of Monsanto: Crops represent potential benefit to the environment

Before the trial Monsanto issued a statement which said: "We regret the breach of consent at the trial in Lincolnshire.

"In co-operation with the DETR and MAFF we took immediate steps to limit any potential environmental impact."

It says that part of a barrier to stop GM pollen getting loose had been mown down by a contractor by accident.

All GM plants were destroyed along with any plants within a 50-metre radius, following the HSE inspection.