Weaning the world off cigarettes is not the most chic of philanthropic causes, but two men with many a coin between them announced yesterday that they were joining forces to focus on helping all of us, whether we live in Bangladesh, Beijing, or Balham, kick the habit.

With the zeal of a teacher sniffing for fumes behind the bike sheds, Michael Bloomberg, the Mayor of New York and founder of the financial news service that bears his name, and Bill Gates, the father of Microsoft, said they were together giving $500m (£250m) to fund anti-smoking campaigns worldwide.

That they think it is an effort worth making is not in question. Indeed, Mr Bloomberg, a former smoker, made a first pledge of $125m two years ago. Yesterday, he said he would add $250m to that sum to be spent over four years. Mr Gates is contributing a further $125m over five years from the Bill and Melinda Gates Foundation.

It is a new departure for Mr Gates, who recently retired from daily duties at the computer software behemoth he created to concentrate his energies on spending the money held by his and his wife's charitable foundation.

While it has long had a focus on eradicating diseases, including malaria and HIV/Aids, it is the first time it has turned its attention to our long-held love of smoking cigarettes.

The World Health Organisation estimates that smoking could kill as many as one billion people this century, mostly in poor and middle-income countries. "Tobacco-caused diseases have emerged as one of the greatest health challenges facing developing countries," Mr Gates said.

Mr Bloomberg's campaign seeks to persuade governments to outlaw smoking in public places, ban advertising to children and help smokers to give up, with initiatives such as the distribution of free nicotine patches.