With the Co-op's decision to refuse to grow GM crops on its 85,000 acres of land, the pressure is growing on supermarkets to clarify their position on GM foods.
BBC News Online asked some of the biggest chains in the country what their policies were.
Safeway removed GM soya and maize ingredients from its own brand products in 1999.
Customers have the choice in certain products to buy non-GM fed alternatives - organic meats, non-GM fed chicken, organic milk and eggs.
It does not intend to "interfere" with the arrangements that branded manufacturers have regarding the sourcing of ingredients for their products.
Safeway's aim is to eventually offer customers all animal derived products from non-GM fed sources.
Sainsbury's said that in response to "overwhelming customer concern and demand for non-GM foods" it was the first major supermarket to eliminate GM ingredients from all its own-brand products. All Sainsbury's own-brand products are labelled to inform customers that they are GM-free.
Waitrose does not sell under the Waitrose label any products which contain or are derived from genetically modified crops. This includes any oils or additives.
Tesco - the UK's biggest supermarket chain - says it already has non-GM feed for poultry and fish, and its organic meat range is from animals fed entirely on non-GM feed.
Asda says its position on GM has not changed since 1998 when it announced its intention to remove GM protein and protein derivatives from all ASDA own-label products. This was completed by October 1999. During the changeover period, the company labelled all products which contained GM ingredients or derivatives. ASDA says it continues to "listen closely to our customers on this issue".
Morrisons has also removed GM ingredients from all of its own-label products.
The Co-op - Britain's biggest farmer - has pledged not to grow GM crops, has banned selling GM food under its own brand products, and will not invest customers' money in GM technology.