Smoking in cars should be banned to protect children and other passengers from the effects of passive smoking, the British Medical Association (BMA) urged on Wednesday.

The concentration of toxins in a smoke-filled car is 23 times that of a bar, according to the BMA. Children are most at risk from secondhand smoke in vehicles, the organisation said, as their immune systems are less well developed and they and are less able to refuse to travel in a car with a smoker. Old people and people with respiratory difficulties are also at high risk.

"Every year in England there are over 80,000 deaths that are caused by smoking. This figure increases to a shocking 6m worldwide," Vivienne Nathanson, director of professional activities at the BMA said in a statement on Wednesday.

"But behind the stark statistics, doctors see the individual cases of ill-health and premature death caused by smoking and second-hand smoke. For this reason, doctors are committed to reducing the harm caused by tobacco.

Smoking was banned in public places in 2007 on health grounds, and the BMA said that the current governments in the UK should take the "courageous step" of extending the ban to include private vehicles.

"The evidence for extending the smoke-free legislation is compelling," Nathanson said. "The current UK Government prefers voluntary measures or 'nudging' to bring about public health change but this stance has been shown to fail time and time again."

In the House of Commons on November 2, Prime Minister David Cameron said that he would have "a serious think" about a smoking ban in private vehicles, following a question from Alex Cunningham, MP for Stockton North. Cunningham's private members bill on the issue is due for a second reading on Wednesday.