Mr Meacher has let a large yowling cat out of the bag

Friends of the Earth

Conservatives accused the government of losing control of the GM issue, and anti-GM campaigners seized on the comments to call for a halt to all UK GM-crop trials.

Mr Meacher said: "It is false to pretend that there is any distance which is going to prevent some contamination."

His comments came during exchanges on a Ministry of Agriculture review of separation distances for GM crops in UK trials.

Mr Meacher went on: "The question is how we can absolutely minimise that to a level which is acceptable to those buying the product, because it is they who buy the product which will have to determine what degree of GM in a non-GM food is acceptable to them."

Call for action

Mr Meacher's aides say experts were already aware of the chances of contamination.

Anti-GM campaigners have long protested about contamination

Separation distances around GM trials can prevent only 99.5% of contamination, so 0.5% of GM pollen could contaminate other crops.

An EU ruling says foods labelled non-GM can contain up to 1% of GM ingredients.

Pete Riley, Real Food Campaigner at Friends of the Earth, said: "Friends of the Earth has long argued that GM pollen spreads further than the biotech industry will admit.

"At last a government minister agrees with us. What we need now is action to prevent the current farm-scale trials and test sites contaminating crops and honey.

"Mr Meacher has let a large yowling cat out of the bag.

"A rambling debate about crop separation distances would be a complete waste of time."

Mr Meacher told MPs that traditional practices dating more than 50 years had established separation distances where 99.5% of pollen would not get beyond those distances.

He said: "The problem is that small and sometimes vanishingly small amounts of pollen may and indeed can get considerable distances and the problem is to know exactly where to draw the line in what is a continuous deposition level over very long periods."

'Threat to consumer freedom'

Shadow agriculture minister Tim Yeo said: "This makes a mockery of all of the government's previous assurances that the environment would be protected.

"They have finally admitted that the farm-scale trials are a potential danger to the environment.

"Farmers and consumers are still reeling from the news that GM contaminated oilseed rape was inadvertently planted in Britain.

"Together with the recent reports that imported maize seeds may also be contaminated, this is one more threat to the freedom of consumers to choose GM-free food.

"It is time for the government to be fully open on this issue.

"For too long they have been trying to cover up the extent of GM contamination in Britain's produce and farmland.

"They have completely lost control of this issue and fail to see how important it is to the British consumer."