Doctors have called on the Government to introduce a ban on smoking in cars.
The British Medical Association (BMA) said the "bold and courageous" move was for reasons of health not safety and urged ministers to bring in the ban.
People who smoke in vehicles expose themselves to large amounts of harmful chemicals with toxin levels 23 times higher than in a smoky bar, according to evidence from doctors.
The increased levels mean that the elderly and children are particularly at risk, it claimed.
The BMA said that children face a higher risk as their immature immune systems are unable to combat the effects of second-hand smoke.
Children also absorb more pollutants than adults, it said.
The elderly face dangers from smoke as they are prone to respiratory issues, which can be exacerbated by breathing in cigarette smoke.
However these groups may be unable to say no to travelling in the car with a smoker, the BMA said.
Dr Vivienne Nathanson, the BMA's director of professional activities, said: "We are calling on UK governments to take the bold and courageous step of banning smoking in private vehicles."
The BMA highlighted its message in a briefing paper launched at the same time as the second reading of a Private Members' Bill, introduced by Labour MP Alex Cunningham, calling for a smoking ban in private vehicles containing children.
However the Prime Minister, an ex-smoker, distanced himself from the Labour MPs proposals, stating that he supported the current ban in public places.
Copyright © Press Association 2011