Some 12 per cent now follow vegetarian or vegan diets – rising to 20 per cent of those aged between 16 and 24, said analysts Mintel.

And millions more are “flexitarians” cutting back substantially on the amount of meat they eat but not quite going the whole hog. Health and environmental reasons are the main factors behind the move, said Mintel’s report to coincide with World Vegetarian Day today.

This has led to a booming £625million-a-year market for meat-free products in 2013, which is expected to grow even more to £657million this year.

Laura Jones, food science analyst for Mintel said: “As World Vegetarian Day arrives, our research highlights just how much of an impact vegetarianism has had on the UK food and drink market.”

She said cutting down on meat was also an ongoing trend, adding: “The meat alternative market will continue to be driven by an emerging consumer trend towards meat reduction on a part-time basis, also called flexitarianism, entailing increased consumption of plant-based foods without completely cutting out meat.”

Mintel estimates that 12 per cent of all new food and drink products launched in Britain this year carry a “suitable for vegetarians” label, compared to six per cent in 2009.

This includes chocolate and confectionary products which now avoid using animal-based ingredients for purposes such as glazing. Laura Jones said: “Among chocolate and sugar confectionery products there is increasingly demand for vegetarian ingredients, reflected by the increasing use of both vegetarian and vegan claims on new product launches.

“Ingredients will continue to be scrutinised by consumers and manufacturers need to be responsive and proactive to quell any consumer concerns.”