
"On the assumption that you wouldn't pass the packet round and invite the kids to light up, why make them breathe tobacco smoke at all?"
He said the Canadian province of New Brunswick, California, South Australia and Cyprus had already introduced such legislation successfully.
And Professor Stephenson said second-hand smoke had been linked to chest infections, asthma and ear problems in children.
Deborah Arnott, chief executive of the anti-smoking charity Action on Smoking and Health (ASH), backed a complete ban on smoking in vehicles.
"Cars are small tin boxes, with not much air in them.