The BBC's June Kelly: "Nearly all of us are regularly eating genetically-modified food"

Consumer, food and environmental groups have reacted by intensifying their calls for a ban. Supermarkets however are sticking by the food already on the shelves.

The largest British food retailer, Tesco, says it will continue to sell such products, which according to European law have to be clearly labelled as such. "We have to leave our customers the choice to decide whether or not they want to buy them," said a spokesman.

Gerry Hodes, from Marks and Spencers, told the BBC: "We satisfy ourselves and take government advice that all our products are safe to eat."

Safeway said it will sell products containing GM ingredients provided they have approval from the appropriate regulatory authorities and "tangible benefits" for consumers.

Safeway added that sales of its GM tomato puree, introduced in February 1996, has outsold its more expensive, conventional counterpart in some stores. More than 600,000 cans have now been sold.

However, Asda said it was working to remove all GM ingredients from its own-brand products. A spokeswoman said: "We have a very clear approach to GMs. We are working to prevent any new GM ingredients being used in all our products. We are reflecting our customers' views."

Only Iceland has a ban on all GM foods in place.

No to GM foods

The Consumers' Association, organic campaigners the Soil Association and the Food Commission are all calling on for government action to restrict GM food.

Calling for a total and immediate ban, Patrick Holden, director of the Soil Association, said: "This announcement vindicates our calls for a complete halt on all GM crop trials in the UK. We are treating our countryside as a laboratory and the human population as guinea pigs. At present the only food guaranteed to be GM-free is organic."

GM food was first sold in the UK in 1996

Tim Lobstein, co-director of consumer watchdog the Food Commission, added that supermarkets should check their legal insurance: "If there are implications for public health in the future as a result of GM ingredients being in the food chain then this may raise the question of legal liability."

Environmental groups also expressed grave fears. Greenpeace campaign director Doug Parr said the Pusztai incident had shown that GM organisms were "unstable" and should be taken out of the food chain.

He said: "We are calling for a total ban on all GM food immediately. If the genetic modification process is causing problems then the Government should apply the precautionary principle."

Friends of the Earth called for an immediate five-year freeze on the licensing and cultivation of GM foods.

Monsanto, one of the world's largest biotechnology companies, has pioneered new GM crops around the word, said that the backing of the research did not dent its confidence in the new technology.

A spokesman said: "We think the products we produce are safe. Every GM food has to go before the regulatory bodies and then be put through a lengthy and exhaustive assessment process."