The British Medical Association (BMA) has called for a "bold" UK-wide ban on smoking in cars.
It is claimed the government's 'nudging' exercises have failed "time and time again" and it is now time for an outright ban.
Research shows the "restrictive internal environment" of cars exposes drivers and passengers to 23 times more toxins than a smoky bar.
The BMA said children in particular should be protected from the dangers of second-hand smoke as they absorb more pollutants and have under-developed immune systems.
"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 Dr 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. 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."
Stockton North MP Alex Cunningham will lead the second reading of a Private Member's Bill calling for a ban on smoking in private vehicles when children are present on 25 November.