Doctors warn that 'part-time' smokers are as at much risk as those on the weed all week

"I'm not a smoker", says James, 27, as he lights up yet another cigarette. "I just smoke when I go out." Trouble is, he goes out a lot.

James, drinking with a group of friends in a noisy London bar, reckons he will get through "about 20" cigarettes on a night out like this - but then won't smoke again for the rest of the week. He is part of the new phenomenon of "binge smokers", people who overdose on nicotine once or twice a week, but do not otherwise smoke.

When ministers rejected a call by the country's most senior doctors last week for a ban on smoking in public places, they may not have known the extent of binge smoking, which has been highlighted as one of the more dangerous, and growing, forms of nicotine abuse.

Professor Stephen Spiro, of the British Lung Foundation, says: "People go out and smoke socially on a Friday or Saturday night and get through about 20 or 30 cigarettes.

"It seems to be a cultural thing - people are becoming very careful about smoking during the working day and weekday evenings, but will then go out and smoke a lot at weekends."

Professor Spiro thinks binge smoking could be more dangerous than traditional smoking habits. "It is much more dangerous to smoke 20 cigarettes in four hours than to smoke the same amount over the course of a day," he says. "The amount of nicotine getting into the bloodstream is much higher. That is an incredible hit on the lungs and the heart."

An estimated 12 million Britons are classified as smokers, with about 120,000 dying as a result of their habit every year. The proportion of women making up this statistic is on the rise. According to Prof Spiro, this year, for the first time, more women than men have died from lung disease.

Dr Roy Bailey, a consultant psychologist specialising in addiction, is one of those worried that binge smoking is part of this disturbing trend.

"These people are living their lives in brackets," he says. "When they go clubbing, they buy fags - it's part of the night out. But they wouldn't define themselves as smokers.

"The trigger for binge smoking is probably alcohol. When you put the alcohol, the location and the people together, you've got a pretty good context for binge smoking - and when you find the right context you can hit one cigarette after another."

At Base, a trendy bar near Westminster, James and his drinking companions were inclined to agree.

"I only smoke if I drink," says Natalie Miller, a shipping executive. "Smoking makes me relax and unwind faster, but I wouldn't say I qualified as a proper smoker. I'll probably get through about 10 cigarettes tonight, but if I wasn't going out it would be more like five a fortnight."

Matt, a 26-year-old civil servant, agreed: "I'm not addicted, but I love to smoke with a beer," he said. "When I go out, I might get through 20 cigarettes in an evening, but I refuse to buy my own, because that would mean I was a smoker. I don't carry a lighter for the same reason."

Lorraine Shepherd, 35, a personal secretary, is also a self-confessed binge smoker. "I don't really know why I do it; it stinks and I think it's disgusting," she says, puffing on a Marlboro Light. "I've got a real thing about the smell. If I'm sober enough when I get in, I'll jump straight into the shower. And the morning after I'll get up, strip the bed and wash all my clothes from the night before."

But while binge smokers seem unconcerned about their habit, experts say it could be just as addictive as more traditional smoking patterns.

Dr Amanda Amos, of Edinburgh university, has conducted two major studies into smoking among young adults.

"Some binge smokers don't even see themselves as smokers," she says. "The idea is: 'how can you be addicted if you're only doing it at weekends?' but research shows that even a small amount of smoking can build up an addiction to nicotine: slowly you slip into it."

Professor Gerard Hastings of the Centre for Tobacco Control Research in Perthshire, Scotland, says a ban on smoking in public places could deal a fatal blow to binge smoking. But the weekend binge smokers aren't bothered. They seem reluctant to admit that the problem has got anything to do with them.

"I'm really up for a ban on smoking in bars," says James, a bottle of beer in one hand and a cigarette in the other. "It doesn't bother me, because I'm a non-smoker."