A year ago, if you'd asked Professor Robert West to predict the effect that the smoking ban in England would have on smokers he would have reckoned on no change. Yet tomorrow, on the first anniversary of the legislation that banned smoking in public places, he will announce that an estimated 400,000 people have given up since it came into force. This represents a dramatic increase in the rate at which regular smokers are quitting.

Smoking rates have gone down by five percentage points over nine months, an average increase of 0.6 per cent each month, compared with 0.2 per cent before the ban. This means that three times as many smokers are now quitting than in the nine months before the ban. “This is not as I expected and it's dramatic,” says West, Cancer Research UK's director of tobacco studies. “Up to April this year, [smoking] prevalence is 4 per cent lower than it would otherwise have been, which we've never seen in this country before.”

West's figures are based on a monthly study of 1,700 smokers throughout England where an estimated 9.5 million people smoke, accounting for 20 per cent of the adult population. “Even at this rate we're talking about 70,000 deaths a year,” says West. Already it is clear that, by reducing passive smoking, the ban is saving lives. There were 1,384 fewer heart attacks in England in the nine months after the ban.

“The reason is that passive smoke is like bad pollution,” West explains. “When people who've got dodgy cardiovascular systems inhale particulate matter at that concentration it can trigger a heart attack immediately. I would estimate that if we stick with what we've achieved, we will save around 40,000 lives over the next ten years from cancer, heart disease and chronic constructive pulmonary disease.”

West's announcement raises the question of what is making unprece- dented numbers of smokers give up. Is it the health risk? Is the increasingly intolerant attitude of non-smokers towards smoking - exacerbated by the ban - playing a part? Has the Government's Stop Smoking Service made a difference? West believes that for many people the ban provided a trigger in a culture that already discouraged smoking through high cigarette prices and an advertising ban.

“Already smoking is being seen increasingly as something that is not very nice and a bit deviant. All the pressures are there in the system and sometimes, like an earthquake, it just needs an extra trigger to release the tension and create that seismic shift.”

If asked why they're giving up - and 70 per cent of smokers say they want to stop - smokers overwhelmingly cite health, either because they are worried about their future or because they have already become ill. Some smokers cite cost, but few say that they feel under pressure to give up. Health professionals are wary of demonising smokers, and playing into the hands of pro-smoking campaigners, and prefer policies that make smoking difficult to any suggestion that smokers are potential pariahs. TV ad campaigns are known to be effective in triggering quit attempts, as is New Year's Day, but what is critical to the success of the attempt is what happens after it has begun, West says.

“People have to make a mental switch that takes them from finding smoking appealing to thinking ‘That's it, I'm not doing that any more'. Suddenly everything becomes possible, which is at heart an emotional change. It's this epiphany that people experience and it's true of all life changes, from giving up alcohol to leaving a partner.”

This is where he believes the Government's stop smoking service is effective, because it provides support from health professionals and access to prescription medication, including nicotine replacement therapy and the new drug Champix, which acts like an appetite suppressant for nicotine hunger. Between 15 and 20 per cent of those who use the stop smoking service are still not smoking after 12 months, which compares favourably with other addictions.

Not that West is complacent. The drop in the number of smokers might not continue, he says, and emerging evidence of regional differences in smoking prevalence shows that there is still research to be done on understanding the motivation behind smoking - and quitting.

In London only 15 per of people smoke, while in Yorkshire and Hum- berside the number of smokers is unchanged since the ban.

“It's perfectly feasible for the whole country to get to the level of London within a few years,” West says. “But it won't happen unless we start looking at the areas of high prevalence, which are mostly in the North. There are definitely regional differences which can't be explained by social class so it must be to do with the cultural influences that exist in these regions.”

After the ban: changes triggered by last year's laws

Since the smoking ban on July 1 last year pubs in England and Wales have been closing at a rate of 27 per week.

Cigarettes sales have dropped 6 per cent. Smokers bought 2.1 billion fewer cigarettes in Britain in the ten months from July last year to April 2008.

£18 million was spent on advertising for nicotine patches, gum and other products to help people to quit in 2007. The Government also invested £6 million in anti-smoking strategies and advice.

The average weight gain from stopping smoking is 6-8kg and is usually permanent.

Smoking costs the NHS about £1.5 billion a year for treating diseases caused by smoking.

About 80 per cent of the price of a packet of cigarettes consists of taxation.

Sixty-seven per cent of people say they do not allow smoking in their home, compared with 61 per cent in 2006. More than 80 per cent of smokers start as teenagers.

In 1948, when surveys were first conducted, 8 out of 10 British men smoked, the highest level recorded. Among women the peak was almost 5 out of 10, in 1966.