1) Lung cancer - 90% of lung cancers are caused by smoking.
2) Bronchitis - 95% of the people who suffer from this disease are smokers.
3) Heart disease - the nicotine and carbon monoxide in tobacco smoke can harm the heart and blood vessels, and smokers are between 2 and 3 times more likely to die of this disease than non-smokers.

In addition the substances in tobacco smoke can cause cancer of the mouth, throat, windpipe, pancreas, stomach, liver, bladder, kidney, cervix, bowel, and ovaries.  They may also cause emphysema and lead to (and prevent the healing of) stomach ulcers. Forty per cent of heavy smokers die before retiring age (65) compared with 15% of non-smokers.  On average people who continue to smoke lose 16 years of life.

Since the early 1970's the proportion of adult cigarette smokers in Great Britain has fallen from over 50%, to about 21% in 2007. Smokers have been a minority (now about one in five) of the adult population since 1976.  It is estimated that there are now over 10 million ex-smokers in the population of Great Britain, and opinion surveys show that over 65% of them say that they found it surprisingly easy to stop smoking.

When people stop smoking they almost immediately start to become free of the pollution from tar, carbon monoxide and other poisons. In addition breathing should start to improve within days, and blood circulation within weeks. For heart disease, the risks reduce quickly, and the chances of getting lung cancer and many other diseases caused by smoking get less and less over the years until, eventually, they are hardly any higher than if they had never smoked.