The fruit, which tastes and smells like a normal red tomato, has been given two genes from a snapdragon flower that produce the dark colour. The distinctive hue is created by antioxidant pigments that protect against diseases including cancer, heart problems and diabetes.

British scientists behind the crop believe their purple tomato is the respectable face of genetic modification and could help convince the public of the benefits of GM food.

But critics say the potential health benefits are a distraction from the harmful environmental side effects of GM farming.

The tomato  -  developed by the John Innes Centre in Norwich  -  contains high concentrations of anthocyanins, pigments found in blackberries and cranberries.

Anthocyanins are chemicals called flavonoids which mop up potentially harmful oxygen molecules in the body. Although they are produced naturally by tomato plants, they are normally found only in the leaves.

The scientists transferred the genes from the snapdragons using specially adapted bacteria.

Professor Cathie Martin, who led the John Innes research  -  the results of which are published today in the journal Nature Biotechnology  -  said one tomato contained the same anthocyanins as a spoonful of cranberries.

'Most people do not eat five portions of fruit and vegetables a day,' she said.

'But they can get more benefit from those they do eat if common fruit and vegetables can be developed that are higher in nutrients.'

The scientists found that mice bred to be vulnerable to cancer lived longer when fed the GM tomatoes. They now hope to test the effects on men at risk of prostate cancer.

Dr Lara Bennett, of Cancer Research UK, said: 'It's exciting to see new techniques that could make healthy foods even better for us.'

But critics warn that genetic modification is tied in with factory farming methods that harm communities  -  and that any seeds from a GM tomato could produce unexpected effects on the environment.

Via Dailymail