All smoking in cars should be banned across the UK to protect people from second-hand smoke, doctors say.
The British Medical Association called for the extension of the current ban on smoking in public places after reviewing evidence of the dangers.
It highlighted research showing the levels of toxins in a car can be up to 23 times higher than in a smoky bar.
But a report by a cross-party group of MPs and peers said non-legislative options should be considered as well.
The All-Party Parliamentary Group on Smoking and Health even said calling for an immediate ban could be "counterproductive" as consensus needed to be built across society before taking such as step.
The group said there should be a consultation on tackling smoking in cars which could look at whether it would be better to have an outright ban, or if more could be achieved by raising awareness about the dangers through education campaigns.
It pointed out that policing a ban on smoking in cars could be difficult.
No part of the UK has yet implemented a ban, although ministers in Northern Ireland have said they will launch a consultation on the issue.
Meanwhile, in Wales a public awareness campaign has begun highlighting the dangers of smoking in cars. Officials have said if that does not succeed over the next three years, a ban will be introduced.
Neither England or Scotland are currently considering introducing legislation at the moment.
But the BMA believes tougher action is needed.
The doctors' union said an outright ban - even if there were no passengers - would be the best way of protecting children as well as non-smoking adults.
It said the young were particularly vulnerable from second-hand smoke as they absorbed more pollutants and their immune systems were less developed.
Research has show that second-hand smoke can increase the risk of a range of conditions, including sudden infant death syndrome and asthma, as well as impairing lung function.
Dr Vivienne Nathanson, head of science at the BMA, admitted introducing a ban would be a "bold and courageous" move.
She added: "The evidence for extending smoke-free legislation is compelling."
While no part of the UK has yet taken such a step, countries elsewhere in the world have.
Some states in Canada, the US and Australia, as well as the whole of South Africa, have introduced legislation, but in each case it has been focused on stopping smoking where children are present.
Instead, the BMA said a complete ban would be better as it would be easier to police. It would also have the added benefit of potentially improving safety as smoking could be a distraction for the driver, the report said.
The recommendation, which was produced after doctors' voted at their annual conference in the summer in favour of their union lobbying for a ban, received some support from other health groups.
However, the likes of Asthma UK and the British Heart Foundation said any ban should only cover children.
But smokers' lobby group Forest said there was "no justification" for a ban at all.
Director Simon Clark said: "Legislation is a gross overreaction. What next, a ban on smoking in the home?"
A spokesman for the Department of Health in England said: "We do not believe that legislation is the most effective way to encourage people to change their behaviour."
He said instead a marketing campaign would be launched in the spring which would focus on the dangers of smoking in the home and car.
- The BMA issued a correction on Thursday retracting the claim that research showed the levels of toxins in a car can be up to 23 times higher than in a smoky bar. Instead it said the risk in a car was 11 times greater. A spokeswoman said the mistake was due to human error, and it had made the amendment after becoming aware there was other research that disputed their original figure.