The Soil Association has won the Prince's support for its campaign urging shops to withdraw modified products from their shelves by 2000.

It is challenging eight store chains to agree to meet the deadline.

In a letter sent to 15,000 homes by the Association recently, the Prince says that experts should not ask if genetically altering food is possible or safe, but whether it is right.

Prince Charles supports organic farming.

The Prince wrote: "I believe that this particular technology is so powerful and so far-reaching that we should seek ways of engaging a wide range of people and interests in a thorough ethical debate about how and where it should be applied."

The Director of the Soil Association, Patrick Holden says the campaign reflects the concerns of shoppers.

"Consumers are alarmed at the prospect of participating in a genetic experiment without their permission, and with no guarantee of a safe outcome," he said.

"There are too many unquantifiable risks involved to justify using genetically-engineered crops, especially since farmers do not need them and they pose a serious threat to sustainable agriculture and biodiversity."

He challenged Tesco, Asda, Sainsbury, Waitrose, the Co-op, Safeway, Somerfield and Marks & Spencer to stop selling food containing genetically-engineered raw materials.

The Soil Association also wants the government to follow Switzerland's lead and hold a referendum on outlawing genetically-modified food.

Most of the genetically-engineered species released so far in America have been developed by major agro-chemical companies trying to win farmers over to their herbicides.