Some 23 per cent of those who claim to have a meat-free diet succumb to the temptations of the occasional sausage or late-night kebab.

Analysis of diet diaries kept by 11,000 people found that almost six in 10 so-called vegetarians ate red meat, poultry or fish during the two-week period of the study.

Only 42 per cent really were vegetarian, with 51 per cent eating fish and one in five owning up to eating poultry, according to data from the TNS Family Food Panel survey.

The proportion of people who describe themselves as vegetarian in Britain has remained static at around five per cent over the last four years.

Juliette Kellow, a dietitian, said: "We have seen something of a turnaround in the public perception of meat. There is more confidence in its safety and quality, and also growing awareness of the nutritional benefits. Atkins and other high protein diets have had an effect and there have been a number of celebrities like Madonna and Drew Barrymore who have abandoned vegetarianism."