Breathing in secondhand smoke massively increases the risk of lung cancer and heart disease, an official report by medical scientists shows.
Passive smoking is harmful to health
Ministers have sat on the results for months amid fears it will fuel calls for a ban on smoking in public places, claim campaigners.
They say there can now be no excuse for not introducing a total ban.
The Department of Health said the report contained no new evidence and simply pulled together available data.
The Scientific Committee on Tobacco and Health (SCOTH) reported to government four months ago. The leaked report updates their previous work warning of the health risks of passive smoking published in 1998.
Pro-smoking campaigners argue that the case against passive smoking has never been properly proved.
A study by the University of California published in the British Medical Journal in 2003 found that the link between environmental tobacco smoke and coronary heart disease and lung cancer may be considerably weaker than generally believed.
But the vast majority of research shows passive smoking is damaging to health, and SCOTH concluded that the evidence published since 1998 reinforced its earlier conclusions.
It is evident that no infant, child or adult should be exposed to secondhand smoke, the report concludes.
Ministers are preparing to publish their long-awaited Public Health White Paper next month, which is expected to include measures to limit smoking in
public places but stop short of a total ban, covering all restaurants and pubs.
A spokesman from the Department of Health said: "Ministers are well aware of the strength of medical opinion on smoking, which has been publicly expressed in many reports and by many organisations, including the British Medical Association.
"Far from ignoring or repressing this, health ministers have been actively engaged in clarifying aspects of the
"The Chief Medical Officer, Sir Liam Donaldson, recommended a ban on workplace smoking in his annual report last year.
"However demands for government action have to be balanced against the rights and responsibilities of individuals.
"John Reid, the Health Secretary, is committed to producing a White Paper on public health shortly which will address all these issues."
Professor John Britton, chair of the Royal College of Physicians' Tobacco Advisory Group, said: "The leaked SCOTH report confirms what all other health organisations have been telling the government over many years - that passive smoking causes death and disease, particularly in bar workers.
"There can now be no excuse for not introducing a total ban on smoking in enclosed public places as soon as possible. The successful ban in Ireland shows the way forward for the UK."
PASSIVE SMOKING RISKS
The latest report says:
Lung cancer increased by 24%
Heart disease increased by 25%
Damaging to infants - lung disease, sudden infant death and middle ear disease
Mr James Johnson, chairman of the British Medical Association, said: "It beggars belief that the Health Secretary is still talking about 'possible' health effects of second hand smoke. What other evidence does he need?"
Deborah Arnott, director of Action on Smoking and Health, said: "This report shows that Britain's leading medical experts have concluded that secondhand smoke is a serious risk to public health.
"It is deeply worrying that the government has sat on this for months; it should have been published in good time to inform debate around the public health White Paper.
"November's White Paper must follow the Irish model and end smoking in the workplace once and for all. The clear lesson of the report is that nothing less will do."
But Simon Clark, director of the smokers' lobby group FOREST, said the reviews by SCOTH were seriously flawed.
"It is simply not true that the vast majority of research shows passive smoking is damaging health.
"There have been almost 150 studies on passive smoking and overall the results are inconclusive."
SCOTH said that overall exposure to second-hand smoke had declined as less people were smoking.
"However, some groups, for example bar staff, are heavily exposed at their place of work and almost half of all children still live in households with at least one smoker," they said.
Paul Burstow MP, Liberal Democrat Shadow Health Secretary, said: "Ministers should introduce a ban on smoking in enclosed public places to protect people working in bars and restaurants from the effects of second hand smoke."
Conservative Shadow Health Secretary Andrew Lansley said: "The public should be given access to relevant information, rather than having it withheld, whilst Ministers delay in deciding what to include in their White Paper."