Researchers concluded that switching to an organic diet would provide an antioxidant boost equivalent to one to two extra portions of fruit and vegetables a day. Their findings were, however, severely criticised by other scientists.

The study was welcomed by Helen Browning, the chief executive of the Soil Association, as “crucially important” in demonstrating that organic food is healthier than non-organic. “It shatters the myth that how we farm does not affect the quality of the food we eat. The research found significant differences, due to the farming system, between organic and non-organic food,” she said.

Professor Carlo Leifert, led the research, which he said demonstrates organically-certified food can improve intake of “nutritionally desirable” antioxidants. “The organic versus non-organic debate has rumbled on for decades now but the evidence from this study is overwhelming – that organic food is high in antioxidants and lower in toxic metals and pesticides,” he said.

Researchers reached their conclusions after analysing data from 343 studies assessing the differences between organic and non-organic fruit, vegetables and cereals. The findings contradict those of a smaller study in 2009 commissioned by the Food Standards Agency (FSA) which found no significant nutritional benefits from eating organic food.

Dr Gavin Stewart, one of the authors of the new report, said: “The much larger evidence base available in this synthesis allowed us to use more appropriate statistical methods to draw more definitive conclusions regarding the differences between organic and conventional crops.”

The study found that concentrations of antioxidant plant compounds such as polyphenolics were 18 per cent to 69 per cent higher in organically grown plants.

Several scientists, however, launched scathing attacks on the research which they said was flawed and misleading.

Dr Alan Dangour, of the London School of Hygiene & Tropical Medicine, was critical of the quality of some of the data used by the researchers and said: “The public health significance of the reported findings have been worryingly overstated. There is no good evidence to suggest that slightly greater antioxidant or polyphenolic intake in the human diet has important public health benefits.”

Professor Tom Sanders, of King’s College London’s School of Medicine, said the study, published in the British Journal of Nutrition, was misleading. He said: “This article is misleading because it refers to antioxidants in plants as if they were a class of essential nutrients, which they are not. The article misleadingly suggest health benefits result from a high consumption of antioxidants, particularly cancer protection.

“This study provides no evidence to change my views that there are no meaningful nutritional differences between conventional produced and organic crops.”

Professor Richard Mithen, of the Institute of Food Research, said: “The references to ‘antioxidants’ and ‘antioxidant activity’, and various ‘antioxidant’ assays would suggest a poor knowledge of the current understanding within the nutrition community of how fruit and vegetables may maintain and improve health.”