Environmentalists are stepping up the pressure on ministers over GM today with the publication of new maps highlighting crop contamination.

Friends of the Earth said their botanical data showed that genetically modified crops could cross-pollinate throughout the country.

The announcement comes in the middle of the government-sponsored national GM debate which is testing public opinion ahead of a decision on whether to license the crops later this year.

Commercial growing of GM oil seed rape in the UK will "almost certainly" lead to widespread GM contamination, according to Friends of the Earth.

The environmental lobby group mapped out the locations of five of the most closely related wild plant relatives to oil seed rape, such as wild turnip and wild cabbage.

The maps show that these species, which are known to cross pollinate with the arable crop, are widespread across the whole country.

If GM oil seed rape is grown practically anywhere in the UK, cross breeding will be almost inevitable, the scientists said.Friends of the Earth's GM campaigner Pete Riley said that ministers need the courage to stand up to biotechnology companies who claim their crops are harmless.

"These maps show that if GM oil seed rape is allowed to be grown anywhere in the UK, it will almost certainly result in widespread GM contamination," he said.

"GM pollen can be carried by the wind, bees and through human contact over vast distances.

"The long-term consequences of this are difficult to predict.

"The government must not allow the biotech industry to experiment with the UK's environment. GM crops must not be commercially grown in the UK."