Smoking in cars carrying children is on course to be banned after MPs voted overwhelmingly in favour of the proposals in the House of Commons.
Lighting up on the school run or family outings can now be made illegal with the Commons vote giving Health Secretary Jeremy Hunt the power to bring in a law.
The vote - passed by 376 votes to 107 - also gave the Welsh government the power to introduce it. Ministers must now decide if they want to make smoking in cars carrying children illegal in Wales.
MPs were given a free vote on the amendment to the Children and Families Bill on Monday (February 10) but Prime Minister David Cameron chose to miss the vote in favour of staying with flood victims in the South West.
The vote split the cabinet with Deputy Prime Minister Nick Clegg and Home Secretary Theresa May joining 102 Tories in opposing the move. Only four Lib Dems - including Mr Clegg - voted against the ban.
The ban will not come into force immediately but once in place it is likely to carry a £60 fixed penalty fine or points on a driving licence - similar to using a mobile phone. Question marks were raised during the debate about how any law would be enforced, similar to concerns over how motorists are policed for offences such as lane hogging or failing to wear a seatbelt.
Figures show that in England more than 430,000 children aged 11 to 15 are exposed to second-hand smoke in cars every week and a similar law already exists in some states in America, Australia, Canada and a few European countries.
Dr Penny Woods, chief executive of the British Lung Foundation, said: "Having campaigned on this issue for many years, we're absolutely delighted that MPs have backed the ban on smoking in cars carrying children. This could prove a great leap forward for the health of our nation's children."
Opposition ministers had described the ban - which was tabled by a Labour peer in the House of Lords - as a "blunt instrument" and stated they preferred the use of public information campaigns to address the problem. But the proposals were surprisingly supported by the Lords in January.
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