The giant chain has joined a Europe-wide consortium of food sellers and producers, which includes Marks & Spencer, to buy non-GM products.

A Sainsbury's spokeswoman said: "Our customers have indicated to us very clearly that they do not want genetically-modified ingredients in their food and we are taking steps to offer that guarantee.

"The consortium will be working with farmers and producers to find a supply of ingredients that can be scientifically assessed to prove that they are GM-free.

Consortium will buy only guaranteed non-GM crops

"It will be introduced into our own-brand ranges as soon as possible."

The consortium - also including French hypermarket retailer Carrefour and Swiss, Belgian, Italian and Irish chains - aims to use its considerable buying power to break the stranglehold US GM-soya producers have on the market.

Independently tested

American soya producers have made it impossible to date to guarantee GM-free food by mixing GM and non-GM soya at source.

Around 50 own-brand products - most of them processed foods including ready-cook meals, biscuits and tomato puree - will gradually be phased out by June, according to Sainsbury's.

The supermarket will also submit its new ingredients for assessment by scientists at independent British firm, Law Laboratories.

The move, which Sainsbury's claims is a "world first", will also see products which could contain GM-derivatives, either replaced with alternatives or phased out.

Friends of the Earth senior food campaigner Pete Riley welcomed the move, saying: "Companies that respect their customers' wish to avoid GM food, and take action to give them what they want, will do better than those who do not.

"The government should assist them by taking action to ban GM ingredients until tests on their potential health impacts have been completed.

"Failing that, ministers must ensure that the public is warned about food products containing any GM ingredients. Anything less will demonstrate how out of touch the government is with the public mood on this issue."

Marks & Spencer and frozen-food chain Iceland are already phasing out GM foods from their own-brand ranges.