Proponents say new technique safer

Modification of foodstuffs and crops is a process that has gone on for thousands of years. Man has always altered food in an attempt to get better crops; to enhance or create flavour - as in the process of fermenting cheese - or to improve storage. Plant breeding involved selecting beneficial traits, such as plants that survived frost better, and discarding lines with negative ones.

Genetically-modified (GM) food brings selection of characteristics on to a new plane. It is produced by a very precise technique of genetic engineering, where a single gene conferring a desirable characteristic is inserted into the myriad of genes that a crop may have.

Its proponents say that selecting a gene which has a particular trait from one species and transferring it into another species of plant, animal or micro-organism can give desired characteristics more safely and accurately than was achieved by the other methods. It can also switch off undesired traits.

Its opponents dispute this interpretation - though it is accepted by the vast majority of the scientific community - saying the risks have not been sufficiently evaluated. They claim there is evidence to show that genes jump from species to species, and hence GM crops may be unstable and threaten the genetic make-up of traditional crops.

The first generation of GM crops - now reaching supermarkets mainly in the form of foods with maize and soya derivatives - focused mainly on conferring traits such as resistance to herbicides, insecticides and diseases. "Nutri-foods", produced by genetic alteration to improve nutritional content, are set to be the new generation.