Members of the House of Lords backed an amendment to the Children and Families Bill by 222 votes to 197. It does not directly ban smoking in cars with children in them.
Instead it backs the principle by giving the Health Secretary a power to bring in regulations that would make it an offence for a driver to fail to prevent smoking where children are present.
Lord Hunt said: "Around one child in five reports being regularly exposed to second-hand smoke in cars with catastrophic health consequences." In Scotland, the LibDems have proposed a ban which would see motorists fined £60 for smoking while carrying a child in their vehicle. The UK Government said it would not rule out legislation.