About 80% of current research in plant biotechnology is directed towards the improvement of food plants.

Thousands of trials of genetically-modified plants have already been carried out, and products are beginning to find their way on to supermarket shelves, following the lead of the first commercially available food - the Flavr Savr tomato introduced in the USA.

In the UK, products using genetically modified soya and maize are relatively commonplace. The supermarket chains Safeway and Sainsbury's also stock a brand of genetically modified tomato paste.

Supporters of genetic modification argue that the techniques will be able to revolutionise food production by the creation of 'super crops' able to provide much bigger yields, to resist pests and pesticides and to thrive on poor agricultural land.

Genetic modification can also allow food to be kept longer, and to ripen more slowly thus increasing its shelf life. It can also allow flavour and nutritional status to be artificially boosted.

Male-only asparagus

Techniques have been refined to produce specific effects. For instance, genetic modification has been used in asparagus to produce the tastier male-only plants.

Other examples include slow ripening broccoli; parasite-free bananas; celery which retains its crispness even when cut and lower caffeine coffee.

Scientists have even produced lettuce designed to have individual portion sized heads.

Experts are also confident they will be able to produce entirely new crops which could benefit other industries such as pharmaceuticals and fuel.

However, opponents of genetic modification claim the techniques pose serious threats.

There is concern that the introduction of genetically-modified plants will disrupt the world's ecological balance and could have long-term effects on population and health.

Genetic pollution

The use of genetically modified soya beans is commonplace

Some genetically modified plants, such as oil seed rape, can cross pollinate with natural varieties, raising the spectre of genetic pollution, and the eventual extinction of natural forms.

There are also concerns about the impact on farming, particularly in developing countries, and of a takeover by the high-tech sector.

Dr Ian Taylor, scientific political adviser for the environmental charity Greenpeace, said there were also serious concerns about the potential impact genetically modified products could have on health.

"We oppose the release of all genetically engineered organisms into the environment and into the food chain," he said.

"There is a huge domain of scientific uncertainty about the impact of these things. No-one is even able to ask the questions about what the impact will be of introducing genes never before part of the human diet."

Serious concerns

Dr Taylor said serious concerns had already been raised over a genetically modified maize produced by the Swiss company Novartis.

The maize contains a gene which can generate resistance to antibiotics, and which the government's Advisory Committee on Novel Foods and Processes has warned could rapidly neutralise medicine.

In a second case, the genetically modified food supplement L-Tryptophan contained a manufactured bacteria implicated in the deaths of 36 people in the USA.

"The industry is driven by an immense commercial imperative," said Dr Taylor.