It will not only brighten up a salad ... but it could also help you live longer. A purple tomato rich in health-giving substances has been created by scientists as a weapon in the dietary war on cancer and heart disease.

The tomato is purple because it contains the same class of health-promoting pigments found in blueberries, blackberries and cranberries. The pigments are thought to ward off some of the most serious diseases associated with a Western lifestyle.

When scientists fed dried extracts of the GM tomato to a strain of laboratory mice with a genetic predisposition to developing cancer, the mice had an average lifespan of 182 days, compared with 142 days for mice fed on a standard diet.

Scientists in Norwich created the purple tomato by inserting two genes taken from the snapdragon plant that regulate the production of anthocyanin pigments, which could protect against certain cancers, cardiovascular disease and the degenerative illnesses linked to ageing.

The researchers found that anthocyanins accumulated in high concentrations within the purple tomato, accounting for about 10 per cent of the dry weight of the plant's ripened fruit.

Although the leaves of tomato plants are able to manufacture anthocyanins, the pigments are not normally present in the fruit. But the additional regulatory genes added to the GM plant triggered overproduction in the tomatoes themselves, which caused them to turn deep purple on ripening.

Professor Cathie Martin of the John Innes Centre in Norwich, where the study – published in the journal Nature Biotechnology – was carried out, said that the GM tomato could result in a wider choice of healthy foods for consumers, although she accepted that it was unlikely to go on sale in Britain in the near future because of widespread public opposition to GM.

Genetic modification: Health-giving foods

*Golden rice: has two added genes to turn on production of beta carotene in the grains, which go a golden colour. Designed to boost dietary intake of vitamin A, deficiencies of which cause blindness, endemic in south-east Asia.

*Vaccine in a banana: scientists are working on edible vaccines in GM bananas. It would be easy to produce and distribute such vaccines. Work is most advanced in creating a banana vaccine against the hepatitis B virus.

*Anti-clotting milk: GM goats have been created that produce certain high-value drugs in their milk, which is processed to extract the medicine. Includes anti-clotting proteins.