Britain faces a choice between organic or genetically modified produce, Michael Meacher has warned.

Speaking during his tour of Canada, the former environment minister argued that evidence of "massive" cross-contamination prevents the two types of cultivation from co-existing.

"The problem is massive," he told the BBC Radio 4 Today programme on Wednesday.

"I have spent the whole day seeing several farms and several examples where tghere has been very extensive contamination, particularly of oil seed rape.

"The fact is that it goes everywhere. There is no question that there can be a short separation distance - that is clearly not the case."

Canadian organic farmers are suing biotech industries after they were prevented from describing their products as "GM free."

"The buzz word in Britain is that we can have 'co-existence' between the GM sector and the organic or conventional sector. What Canada shows, who have been trying to do this for the last seven years, is that it is absolutely impossible," added Meacher.

"You have to make a choice, and the choice frankly is: are we going to go for GM, for which there is no market and no-one wants to buy at the expense of organic, which people do want to buy and for which there is a tremendous market.

"You cannot have both."

The MP for Oldham West and Royton argued that oil seed rape could blow in the wind "over considerable distances."

"Canada was very favourable to GM," he said.

"They believed Monsato and the other big companies when they said there would be increased yields, less use of herbicides and there wouldn't be a problem with contamination.

"Every one of those has turned out, in their view, not to be justified so I don't think the scorecard shows there are significant gains."

In response, the Liberal Democrats argued that Meacher's comment was sound advice for the British government.

"If they can't find adequate separation distances for GM and non-GM crops in a country larger than the EU, then there's little hope of resolving problems on an island the size of Britain," said rural affairs spokesman and St Ives MP Andrew George.

"The Canadians are in a bind. They have created an irreversible environmental hazard, and are having severe problems finding a market for the GM products.

"The government's approach to GM is turning out to be a classic no-brainer. The public are being invited to take a risk for no obvious benefit.

"The issue is no longer whether there are environmental hazards, but whether the government can face down pressure from the biotech giants and the United States."