Author of the study Dr Carlos Dora explains his findings

A study looking at France, Austria and Switzerland found that the number of people dying from respiratory or cardiovascular problems which could be attributed to car fumes far outweighed the death toll from crashes.

The BBC's Richard Hannford: "Vehicle pollution is responsible for an extra 21,000 deaths"

The WHO will now ask 70 environment and health ministers gathering for a conference in London to adopt a new charter on transport policies to reduce the effects of pollution.

Dr Carlos Dora from the WHO European Centre for Environment and Health said: "The growing evidence that air pollution is causing a major health burden adds to effects of road traffic through noise, accidents and barriers to cycling and walking.

Roger Higman, Friends of the Earth: Pollution builds up rapidly to unhealthy levels

"We are paying a huge price for this excessive road transport with our money and our health."

The research found that one third of all harmful particulate air pollution was caused by road transport, and that long term exposure to pollution caused an estimated 21,000 premature deaths a year across the three countries.

This is far higher than the 9,947 who died that year as a result of road accidents.

Bill runs into billions

In addition, the researchers calculated that the car fumes caused 300,000 extra cases of bronchitis in children, and 15,000 extra hospital admissions for heart disease made worse by the pollution.

They calculated that the cost of dealing with all this was �27 billion Euros per year - about �16bn.

But a British GP, a former chairman of the GPs in Asthma group, said that while car pollution worsened existing asthma, there was little evidence that it actually caused the condition.

Dr Dermot Ryan, a Loughborough GP, said that the focus should fall instead on cigarette smoking as the primary villain.

"I'm not too sure car pollution is the number one enemy. 400 people a day are dying in this country due to cigarette smoking," he said.

He recalled a recent study that compared the incidence of asthma between Munich, a fairly non-polluted city, and Leipzig, a city with a large degree of particulate-producing heavy industry.

Asthma was found more widespread in Munich, he said.

"It's difficult to prove this cause and effect, whereas we can prove passive smoking is very, very damaging to children, and actually causes asthma."

Pets, cookers and carpets to blame

Studies have linked a number of other factors with childhood asthma, among them not breastfeeding, smoking while pregnant, carpets, gas cookers, and pets.

Roger Higman, of Friends of the Earth, said that it was clear to his organisation that fumes were at least as big a killer as road traffic accidents.

He said: "What this research shows is that air pollution is a serious problem - and should be treated as such.

"A lot of money goes into making cars more safe, but not as much is spent tackling air pollution."