The ban on smoking in public places in England has come into force.
Now a thing of the past
Supporters say the step is vital for public health, while critics dismiss it as unnecessary.
Here a panel of experts give their views.
Ruairi O'Connor, British Heart Foundation
Lord Wakeham, Economic Affairs Committee
Jean King, Cancer Research UK
Dr Geoffrey Kabat, Albert Einstein College of Medicine
Dr Keith Prowse, British Lung Foundation
Simon Clark, Forest
Sir Richard Peto, University of Oxford
Sir Liam Donaldson, Chief Medical Officer for England
Public Affairs Manager, British Heart Foundation
"Smoking is one of the major risk factors for heart disease, and second-hand smoke has been proven to be a significant contributory factor as well.
"A number of studies have shown an increased risk of coronary heart disease in non-smokers who live with a smoker.
"And exposure to even small amounts of smoke can have a big impact - even half an hour's exposure to second-hand smoke is enough to damage the lining of your arteries.
"And we know that looking solely at the workplace, second-hand smoking causes at least 600 premature deaths every year - almost three times the number killed in industrial accidents.
"On that basis 600 workers' lives should be saved every year as a result of smoke-free workplaces.
"But if you start looking at the knock on effects on people who give up smoking as a result of the ban, it's more.
"It is estimated that there will be between 600,000 and 800,000 potential quitters, after the ban.
"So if all the people who say they are going to, give up, we would see a large number of people living longer and healthier lives.
"There could be a significant impact on the health of the smokers themselves and those that might be subject to their second hand smoke."
Economic Affairs Committee
"The foremost authority in this area - Sir Richard Peto, professor of medical statistics at Oxford - told the Committee that the risks from passive smoking are small and difficult to measure.
"Given the miniscule level of risk, the blanket ban on smoking in public places is a case of using the proverbial sledgehammer to obliterate, rather than crack, a rather small and insignificant nut.
Lord Wakeham is unconvinced
"As the risks from passive smoking are tiny, the direct impact on public health is likely to be so small as to be immeasurable.
"However, indirect effects are more difficult to determine.
"It may lead to people smoking more at home which becomes one of the few places where smokers can light up.
"This could lead to more passive smoking by children for whom some have argued the health risks may be greater.
"Some claim that one advantage of the ban is that it will encourage more people to quit smoking by making it much more difficult for them to light up.
"If that happens then it could boost public health.
"However, the government has always made clear that getting people to quit smoking is not one of the policy's objectives."
Director of Tobacco Control, Cancer Research UK
"This is the single most important public health measure for a generation, because the immediate effect is that it will protect workers around the country from the harmful effects of passive smoke.
"From experience elsewhere we know that people will also use it as motivation to try and quit smoking.
"Long term, the ban will help promote the perception, especially among young people, that smoking isn't a normal thing to do.
"The more we have a smoke-free world out there then the less likely it is young people are going to be tempted to start smoking.
"So it's a ripple effect, it starts with the people we're trying to protect immediately, the workers, and then the smokers who will try and give up, then there's the bigger effect on society as we become a smoke free society."
DR GEOFFREY KABAT
Albert Einstein College of Medicine, New York
"I did a study of people who had originally enrolled in a large American Cancer study.
"We followed as many people as possible for 38 years and asked whether, among non-smokers, did those married to spouses who smoked have a different mortality to those whose spouses didn't smoke?
"Our report, although it was a carefully done analysis in the British Medical Journal, made people unhappy because it didn't show an effect of passive smoking on the risk of developing heart disease.
"Different studies have shown different results, but when you have a weak effect of anything, some studies will show an effect and others won't.
"Another problem with these studies is that it's difficult to measure how much smoke people are actually exposed to - we don't even know how much a smoking spouse is in the presence of a person.
"This means one has to be very cautious when interpreting these studies - the fact that you do or don't find an effect of passive smoking is questionable and you can't be categorical about its effects.
"So we can't say with certainty how beneficial a public smoking ban will be in terms of passive smoking, but it does make it harder to smoke so it could be a tool for helping people.
"And there is every reason to believe that some people, like asthmatics, will benefit from it."
DR KEITH PROWSE
Chairman, British Lung Foundation
"The biggest effect would be to ban smoking in the home.
"That's not really a feasible proposition, but that's where most small babies and toddlers get their biggest exposure to smoke, and there's no doubt that it is significantly harmful to them.
"But the public ban will make life a lot more comfortable for small children when they are out in public places, particularly if they have lung problems, because smoke can aggravate asthma, cystic fibrosis and bronchitis, and increase incidence of infections.
"So if children are exposed to smoke in public places very much then the ban should reduce the incidence and the severity of all of these things very considerably."
Director, Freedom Organisation for the Right to Enjoy Smoking Tobacco (Forest)
"I think the smoking ban is going to have relatively little impact on public health.
"People say that 11,000 non-smokers die every year in the UK from passive smoking, and 600 of those are people who are allegedly exposed to smoke in the workplace.
"But these figures are estimates, calculations, they are not based on any hard evidence.
"If passive smoking is a risk to people's health, and it's a massive if, it's far more likely to be a risk in the home than in a well-ventilated bar or restaurant.
"And after the ban more people are going to smoke at home, so the ban could potentially make things worse.
"Of course it will help some people who wish to cut down or quit, but the reality is that very few people will.
"I don't smoke, but I'm overweight, and if I was asked, 'Do you want to lose weight?' of course I'd say yes, but that doesn't mean I'm actually going to do anything about it.
"Smokers are the same, they will often say, 'Yes I'd like to cut down a bit,' but the reality is the vast majority of them don't.
"And in Ireland, smoking rates are now exactly the same as they were before the ban there.
"So the idea that millions of people are going to give up smoking is fantasy."
SIR RICHARD PETO
University of Oxford
"Cigarette smoke is the most important cause of cancer in the world and so the exposure of non-smokers to it is going to cause some risk of death.
"But there is reasonable disagreement as to how big that risk is: smokers kill more smokers than non-smokers.
"However, if this ban helps people who want to stop to manage to do so then it could save a lot of lives and prevent a lot of premature deaths.
"Smoking is still responsible for about 20-25% of all deaths in middle age, and most smokers who die in middle age wouldn't have died if they hadn't smoked.
"Half of all smokers are going to be killed by tobacco. If a million people stop smoking who wouldn't otherwise have done so then maybe you'll prevent half a million deaths.
"One other group that gets ignored is ex-smokers - they have got some damage to their lungs already so they're half way to getting cancer.
"If they don't get extra exposure then they may well avoid getting the disease, so the ban will protect them."
SIR LIAM DONALDSON
Chief Medical Officer for England
"The impact of the new smokefree law cannot be over-estimated.
Sir Liam believes the ban is highly significant
"It is one of the most significant public health reforms in England for decades and will create the single biggest improvement in public health for a generation.
"Second-hand smoke is a killer. It contains more than 4,000 chemicals - more than 50 of which are cancer causing - and causes a number of serious medical conditions including heart disease, lung cancer, sudden infant death syndrome and asthma attacks.
"There is no safe level of exposure in enclosed environments and the new law recognises that fact.
"Over time, thousands of lives will be saved thanks to the introduction of smokefree environments, through reduced exposure to second-hand smoke and a reduction in overall smoking rates.
"Many thousands more lives will be spared the misery of watching friends and family die prematurely from smoking-related illnesses."