Britain should introduce a ban on all smoking in cars to protect people from second-hand smoke, a leading doctors' union said Wednesday.
The British Medical Association (BMA) urged the government to take a "bold and courageous step" and extend current laws to include a ban on smoking in private vehicles.
Britain banned smoking in public places such as pubs and restaurants in 2007 but has avoided legislating for private areas.
"The UK made a huge step forward in the fight against tobacco by banning smoking in all enclosed public places, but more can still be done," said Vivienne Nathanson, the BMA's director of professional activities.
"We are calling on UK governments to take the bold and courageous step of banning smoking in private vehicles. The evidence for extending the smoke-free legislation is compelling."
Children and elderly people are the worst affected, especially because they are often unable to refuse to take a journey in a smoky car, the BMA said.
It cited research as showing that levels of dangerous toxins in cars can be 23 times higher than in a typical smoky bar.
Around 4,000 adults and 23 children die each year as a result of second-hand smoke in Britain, the BMA said.
The British parliament is due on November 25 to debate a bill calling for a smoking ban in private vehicles when children are present.
Prime Minister David Cameron, a former smoker, has said he supports the smoking ban in public places but is "nervous about going into what people do inside a vehicle."
British smokers' lobby group Forest said the evidence that smoking in cars is harmful to other passengers is "weak".