The Co-op has announced that it is banning genetically modified food and ingredients throughout its entire business.
Some fear GM crops could damage wildlife
The company, which owns farms, supermarkets and a bank, has said it has taken the decision as a result of a survey of its customers.
Animals on its 85,000 acres of farms will not be given GM feed, the firm says.
It is banning GM from its entire business after four-fifths of Co-op customers surveyed said they would not knowingly buy food containing GM ingredients.
The Co-op will also refuse to grow GM crops even if the government insists it is safe.
The groups move is likely to put pressure on other supermarket groups to eliminate GM ingredients from their food produce.
Tesco - the UK's biggest supermarket chain - says it already has non-GM feed for poultry, eggs and fish, and its organic meat range is from animals fed entirely on non-GM feed.
In 1998, Iceland became the first retailer to remove GM ingredients from its own-label products.
Last week, a major environmental-impact study of GM crops found an oilseed rape and a beet crop to be more harmful to many groups of wildlife than their conventional equivalents.
The results of the crop trials, although mixed, were portrayed in the media as a massive blow to efforts to introduce commercial farming of GM.
The Co-op survey, done over the weekend by NOP World, suggested 55% of people were against GM with 38% yet to be convinced of its benefits.
And 78% were yet to be convinced that the commercial growing of GM crops should be allowed in the UK.
Martin Beaumont, chief executive of the Co-operative Group, said: "On the strength of current scientific knowledge and the overwhelming opposition of our members, the
Co-op is saying no to commercial growing of GM crops in the UK.
"And we would urge other consumer-led businesses to follow this precautionary approach. Too little is still understood about this technology and how it would impact on our environment in future generations.
"Let the science and research continue, but unless or until the case is convincingly made, the government has a responsibility to keep the lid on commercial growing."