Second-hand tobacco smoke at work kills hundreds of Britons each year - including almost one hospitality industry worker a week, a study says.
The government is reluctant to ban smoking in the workplace
Thousands more are dying from passive smoking at home, according to researchers at Imperial College London.
The figures were released ahead of a conference on smoking in London.
Doctors said they highlight the need for a workplace smoking ban, but pro-smoking group Forest called for hard evidence passive smoking was a killer.
Professor Konrad Jamrozik looked at the number of people who died from lung cancer, heart disease and stroke in England and Wales in 2002.
He then calculated how many of these would have died as a result of being exposed to second-hand tobacco smoke using a special mathematical formula.
This formula was based on information from other studies on the risks of dying from lung cancer, heart disease and cancer as a result of passive smoking.
About 30% of adults under the age of 65 smoke. An estimated 42% of people under the age of 65 are exposed to tobacco smoke at home and 11% at work.
According to Professor Jamrozik's calculations, approximately 700 people die from lung cancer, heart disease or stroke because of passive smoking at work.
Another 3,600 people die as a result of second-hand smoke at home.
He also estimated that passive smoking kills one person working in the hospitality industry every week.
Professor Jamrozik said the figures were probably the most accurate estimates available at the moment.
"In the absence of a direct observational study, I feel this research is the best evidence we have in this country to show the effects of passive smoking in the workplace," he told the BBC.
Professor Carol Black, president of the Royal College of Physicians, urged the government to ban smoking in workplaces.
"Environmental tobacco smoke in pubs, bars, restaurants and other public places is seriously damaging to the health of employees as well as the general public.
"Making these places smoke-free not only protects vulnerable staff and the public, it will also help over 300,000 people in Britain to stop smoking completely."
However, Forest rejected that idea.
"Once again we are presented with estimates, calculations and 'likely risk'," said Simon Clark, its director.
"Where is the hard evidence that passive smoking is killing people? If one person dies every week from passive smoking at work, as the anti-smokers claim, it's time to name names.
"Let's have proof, not statistics based on very dubious science."
He added: "A total ban on smoking indoors should be a last resort, not a first option.
"What's wrong with a choice of designated smoking areas or better ventilation that allow people to smoke without bothering non-smokers?"
The UK government has so far resisted calls to ban smoking in the workplace. This is despite calls to do so from the chief medical officers of England and Scotland.
Ministers have said they prefer a voluntary approach rather than following Ireland and introducing a ban.