A ban on smoking in cars with children present has moved a step closer after peers inflicted a defeat on the Government in the House of Lords.
Campaigners welcomed the result of the Lords vote, claiming a ban would protect half-a-million children who were exposed to second-hand smoke in cars every week.
Although the successful Labour amendment to the Children and Families Bill does not directly ban smoking in cars with children in them, it backs the principle of making it an offence.
It gives Health Secretary Jeremy Hunt a power to bring in regulations that would make it an offence for a driver to "fail to prevent smoking in the vehicle when a child or children are present".
The move could become law as Government sources indicated that MPs will be given a free vote on the issue when it returns to the Commons.
The Labour move was backed by 222 votes to 197, majority 25, in the House of Lords.
There were 28 Liberal Democrat rebels on the amendment, including former Cabinet ministers Baroness Williams of Crosby and Lord Rodgers of Quarry Bank.
The amendment was also supported by 148 Labour peers, 34 crossbenchers, 11 others and the Bishop of St Albans.
The opponents of the amendment were 136 Tories, 26 crossbenchers, Labour peers Baroness Golding and Lord Howie of Troon, 29 Liberal Democrats and four others.
Shadow public health minister Luciana Berger said: "The Government should accept that tonight's defeat sends a clear message - we need action to put children's health first.
"When it comes to the Commons next month, Ministers, as well as Tory and Liberal Democrat MPs, should show they recognise that this issue cannot be ignored and not try to kick it into the long grass."
British Lung Foundation chief executive Dr Penny Woods said: "We are absolutely delighted that the House of Lords has voted in favour of this move towards banning smoking in cars when children are present.
"If enacted a ban would help protect the nearly half a million children who are exposed to toxic second-hand smoke in a car every week.
"This is an issue that the British Lung Foundation has been campaigning on relentlessly. We now look to the Government to listen to the overwhelming support shown across the House of Lords for a ban and take the necessary steps to protect our children's health".
Baroness Finlay of Llandaff, a former president of the Royal Society of Medicine, said: "A child in the back seat belted in is effectively imprisoned in the vehicle for their own safety while travelling, but they really are stuck there.
"Whatever adults do they have no control over. But it is also worth remembering that they don't feel able to say anything."
Broadcaster Floella Benjamin said more than 800 children a day went to see doctors with problems associated with second-hand smoke.
Baroness Benjamin, a Liberal Democrat peer, said: "Let's take careful consideration as to what action we should take to protect from the result of second-hand smoking and act robustly in the best interests of the child."