Making jokes about veganism is hardly likely to result in a mass walkout. But Higgins has taken comfort from knowing that at least people know what it is.

When the 33-year-old animal rights campaigner adopted the more extreme version of vegetarianism in 1988, her new-found beliefs met with perplexed looks. "When I said I was a vegan people would look at me as if I had just said, 'I'm from the planet Mars'."

The transformation of veganism from oddball movement to the fringe of the mainstream has taken 60 years. Its progress to the mainstream is likely to be much quicker.

There are estimated to be at least 600,000 vegans in the UK, although there may be up to one million. The number is certainly growing sharply. Food surveys suggest that there were just 100,000 in 1993 The vegan movement was started by a woodwork teacher, Donald Watson, in 1944 because of a desire to improve animal welfare. Watson grew up on a farm in South Yorkshire in the 1920s and became concerned for animal welfare when his Uncle George slaughtered one of the farm's pigs.

He recalled in an interview aged 92 (three years before his death): "I decided that farms . . . and uncles . . . had to be reassessed: the idyllic scene was nothing more than death row, where every creature's days were numbered by the point at which it was no longer of service to human beings."

Watson became a vegetarian and later a vegan, a word he invented.

The central tenet of the lifestyle and philosophy is that human exploitation of animals, as fellow sentient beings, is wrong. Vegans do not eat meat or fish and they also dislike the cruelty of dairy farming, which produces milk from cows with swollen udders who are separated from their new-born calves, of which the males are killed or shipped for veal.

They dislike the conditions of poultry farming and the fact that the eggs eaten could have become chickens themselves.

Veganism has a surprisingly large number of celebrity followers . . . some of them with public images far removed from the sandalwearing stereotype. Wikipedia, the online encyclopaedia, has a veritable roll-call of celebrity vegans. Woody Harrelson, the actor, is a vegan, as are his fellow Hollywood stars Joaquin Phoenix, Alicia Silverstone and Gwyneth Paltrow. The singer Bryan Adams refuses to eat milk or cheese or any other animal product, as do k d lang and Moby.

Heather Mills-McCartney, the wife of Paul McCartney, himself a vegan, is the latest celebrity convert to the cause. The former model announced her conversion last August, saying that vegetarianism not only benefited health but also made a huge difference to the planet.

She added: "I could never go back to eating meat or fish and I'm moving towards being vegan. When I crack an egg now, I think: 'Could that have been a baby?'" Vegans eat all the foods meat-eaters eat . . .

except meat, poultry, fish, cow's milk, yoghurt, cheese and honey. They also avoid wearing leather, bone, ivory, feathers, and mother of pearl. They use all manner of combinations of vegetables and pulses to replace animal-based ingredients in food.

A commercial market has also emerged in free-from foods suitable for vegans and for people who cannot eat dairy products for health reasons. This sub-sector of the food industry is booming.

Holland & Barrett, the health food shop, stocks more than 1,000 ranges of vegetarian foods. Many of them are vegan, such as the Sos Roll and the Porkless Pie. "They are selling incredibly well, " said Lorna Pridmore, the chain's food buyer, who credits part of the success of meat-less whole foods to the TV nutritionist, Gillian McKeith.

"We saw a huge lift in sales last year and generally the food side of the business is growing rapidly. We have so many products that we want to put in but we are running out of space."

One of the biggest producers of vegan fare, Plamil Foods, has seen revenues rise by between 10% and 15% a year. Its 30 products are made at its meat and dairy-free factory in Folkestone, Kent. One of the company's best-selling products is egg-free mayonnaise, made from water, oil and pea protein instead of eggs.

The managing director, Adrian Ling, has noticed a considerable change in perceptions of veganism in his 23 years at the company, which began making soya milk. "There has been a vast change. As veganism has grown, understanding of it has grown. The word vegan is commonplace and the food has become widely available in supermarkets.

"Whereas a long time ago it was perceived as food for sandal-wearers, it's now become more mainstream."

The rising number of vegans has also reached a critical mass.

"Not having dairy when you are eating out is much more easy, " explains Catriona Toms, of the British Vegan Society, which has 5,000 members. "People are becoming much more aware of lactose intolerance and places like Starbucks have soya milk, as do all the main coffee chains." She believes the vegan movement taps into many of the trends which are influencing modern cooking, from the growing interest in animal welfare to awareness of the environment.

Moreover, almost all restaurants have dishes that are, or can easily be made, vegan.

"Indian restaurants don't need to be a problem; Chinese restaurants are the same. In pizza restaurants, you have to be a bit vigilant about what they put in the dough. But anywhere that can cater for vegetarians can cater for vegans if they want to."

There are also vegan-friendly restaurants such as Cornucopia, Cafe Fresh and Govinda's (see Chris Binchy's review on page 24) in Dublin and Cafe Paradiso in Cork.

Vegan diets are healthy, according to followers of the philosophy. The only vitamin from animals that cannot be replicated elsewhere is B12 . . . important for the nervous system and preventing iron deficiency and anaemia. Vegans take supplements, but can also find B12 in food fortified with vitamins such as breakfast cereals.

Such is the rise in veganism that people are no longer bemused by its existence, according to Wendy Higgins, a former campaign director for the British Union for the Abolition of Vivisection. She turned vegetarian aged 10, and vegan aged 16. She explained:

"When I was a child we kept lots of animals, including a cat, guinea pigs and hamsters, and it made no sense to me that there were lots of animals that you cared for, and often cared for very deeply, and other animals that are killed and consumed."

When she became a vegan, life was harder but once the adjustment was made, things became surprisingly easy and have become easier all the while. "I do 99% of my shopping in a supermarket like everyone else, but instead of buying dairy milk I buy soya milk.

Even my local corner shops does soya milk.

"If you are shopping for a low-fat diet or a nut-free diet you just get used to what you can buy and it's not a big deal."

She adds: "People ask, 'What do you eat?'

and they seem to think I must eat carpet or twigs. But I probably eat 80% of what they eat."

CELEBRITY VEGANS

Woody Harrelson Harrelson, 44, who starred in the hit comedy Cheers! and The People vs Larry Flint, has not eaten meat for 15 years. Not only is he vegan, but he also eats a 90% raw diet. At opening night parties, he grazes on vegan canapes and regularly fasts, taking up to a week off from solid food. During one fast he lost 15lb.

He has declared dairy to be one of the great evils of the world. "Yeah, milk does a body good . . . if you are a calf, " he says. "It is evil to your body to put something in there that's designed to make an animal go from very small to very big in a short time."

Gwyneth Paltrow The Oscar-winning actress, 33, lives on a macrobiotic diet of wholegrains, vegetables, beans, seaweed and soya. A lover of new-age treatments, she is married to the Coldplay singer, Chris Martin. Her daughter, Apple, had a vegan first birthday party last year with food and chocolate cheesecake from Moby's cafe, Teany. " I would rather die than let my kid eat instant soup, " she says. She has admitted that people do not see her and her husband as the epitome of rock'n'roll. "There is this perception of us like, 'Oh, they're quite boring, they do yoga and stay home', " she said.

Moby The singer, 40, a "vegan fascist" for nearly two decades, owns Teany, a cafe in New York, which has spawned a vegan soft drinks company.

Moby, born Richard Melville Hall, feasts on vegan focaccia with roasted onions.

"When I think of the fact that literally tens of billions of animals are killed nearly every year for human purposes, part of me wants to go out and join the Animal Liberation Front, " he has said. He admits that some people are filled with "ridicule" at the idea of veganism. But he says that it is "second nature" to him.