At least one-third of early deaths could be prevented if everyone moved to a vegetarian diet, Harvard scientists have calculated.

Dr Walter Willett, professor of epidemiology and nutrition at Harvard Medical School said the benefits of a plant-based diet had been vastly underestimated.

Recent figures from the Office for National Statistics suggested that around 24 per cent or 141,000 deaths each year in Britain were preventable, but most of that was due to smoking, alcohol or obesity.

But the new figures from Harvard suggest that at least 200,000 lives could be saved each year if people cut meat from their diets.

Speaking at the Unite to Cure Fourth International Vatican Conference in Vatican City, Dr Willett, professor of epidemiology and nutrition at Harvard Medical School said: “We have just been doing some calculations looking at the question of how much could we reduce mortality shifting towards a healthy, more plant based diet, not necessarily totally vegan, and our estimates are about one third of deaths could be prevented.