A ban on smoking in cars in England when children are passengers was overwhelmingly supported on Monday night by MPs of all parties.
The move was approved by 376 to 107, a majority of 269, in a free vote which had divided the Cabinet.
The result gives Jeremy Hunt, the Health Secretary, the authority to make it illegal to light up in a vehicle where a child is present but it does not compel him to bring in the legislation.
The vote came after 700 health experts wrote to MPs urging them to support the move. They said hundreds of thousands of youngsters would be saved from exposure to smoke once the practice was outlawed.
Similar bans are already in place in the United States, Canada and Australia.
David Cameron missed the vote because he was in the South-West visiting areas hit by flooding, but signalled his backing for a ban. His spokesman said he believed the move was an idea “whose time had come”.
A ban was also supported by Mr Hunt and Michael Gove, the Education Secretary.
Critics have argued the move would be impractical and unenforceable and would amount to an infringement of personal freedom. Theresa May, the Home Secretary, and Chris Grayling, the Justice Secretary, were among opponents of the move within the Cabinet.
The Liberal Democrat leader, Nick Clegg, the Deputy Prime Minister, has also spoken out against a measure that would “sub-contract responsible parenting to the state”.
Dr Penny Woods, chief executive of the British Lung Foundation, expressed her delight at the vote, which came in a Labour amendment to the Children and Families Bill.
She said: “The introduction of a law that would help prevent hundreds of thousands of children from being exposed to second-hand smoke in the car is now within reach.
“With both Houses of Parliament having made their support for the ban clear, the onus is now on the Government to act accordingly and make this crucial child protection measure law at the earliest opportunity.”
The charity estimates that more than 430,000 children aged 11 to 15 are exposed to second-hand smoke in cars every week in England.
Last night Luciana Berger, the shadow health minister, urged the Government not to delay the introduction of the measure.
She said: “It is a matter of child protection, not adult choice. The will of Parliament has been clearly expressed today and this must be respected.
“Ministers now have a duty to bring forward regulations so that we can make this measure a reality and put protections for children in place as soon as possible.”
A Department of Health spokesman said: “Second-hand smoke is harmful to children and it is right this has been debated in Parliament. We will now determine how this amendment should be taken forward.”
He added that Public Health England would continue its campaign to “ensure parents fully understand the dangers of second-hand smoke and are encouraged to stop smoking in the home or car if there is a child present”.