Second-hand smoke, such as that found in smoke-filled rooms or cars, can impair breathing within 20 minutes, new research suggests.

Even after just a few minutes of exposure, people exposed to the smoke showed near immediate physiological changes that caused their airways to narrow, making it more difficult for the body to take in the oxygen it needs.

Lead reseacher Panagiotis Behrakis, of the University of Athens, said: 'Bars and cars are places where high concentrations of fine particles usually occur because of smoking.

'Non-smokers are then forced to inhale extreme amounts directly into their lungs.

'These results tell us that even a short exposure is indeed harmful for normal airways.'

Although exposure to second-hand smoke appears to be slightly less harmful than direct smoking, Dr. Behrakis believes second-hand smoking should be recognised as a global health issue.

He said: 'Second-hand smoking is the most widespread form of violence exerted on children and workers on a global level. The whole issue needs to be recognised as a global problem of human rights violation.'

The British Lung Foundation says around 300,000 GP visits a year result from the exposure of children to second-hand smoke.

In order to test the effects of short-term second-hand smoke exposure, Dr Behrakis and his colleagues from the Harvard School of Public Health, exposed 15 healthy participants to air heavily concentrated with smoke particles within an exposure chamber - simulating a bar or moving car - for 20 minutes.

Results showed that short-term exposure to concentrated second-hand smoke significantly and immediately impacted participants' airways, making them narrow and reducing the body's oxygen intake.

The Greek study was presented at the annual meeting of the American College of Chest Physicians.

Commenting on the research, Dr Penny Woods, chief executive of the British Lung Foundation said: 'This research suggests that just a short exposure to concentrated second-hand smoke, of the kind you might experience when travelling in a car in which someone has smoked, can be enough to cause your airways to narrow, making it more difficult for your body to take in the oxygen it needs.

'Findings such as these are of particular significance to children travelling in cars in which an adult has smoked, as their breathing is faster, their lungs and immune systems less developed, and the effects of narrowing likely to be greater on their smaller airways.'

This research is the latest in a series of studies into the short and long- term effects of passive smoke in confined spaces, which have united the medical community and charities such as the British Lung Foundation in calling for legislation to ban smoking in cars with children on board.

Dr Woods added: 'Legislation is scheduled to be discussed in the House of Commons next week, and we hope MPs take this opportunity to protect the health of our children - just as they helped protect the health of adults in the workplace with the smoking ban in 2007.'

Last month scientists at Northumbria University reported that non-smokers regularly exposed to second-hand smoke were at risk of damaging their memory. The study was the first of its kind first to explore the relationship between second-hand smoke and memory problems.

They compared a group of current smokers with two groups of non-smokers - those regularly exposed to second-hand smoke and those who were not.

Non-smokers exposed to second-hand smoke forgot almost 20 per cent more than the non-smokers who were not exposed.