Medical experts have called on the government to extend the smoking ban to include cars with children.
A survey has found that over half of children aged eight to 15 have been exposed to cigarette smoke in cars and 86 percent of kids want it stopped.
The British Lung Foundation, which commissioned the survey of 1,000 children in January, has handed in a petition to No.10 with 15,000 signatures asking ministers to look again at smoking legislation and extend the ban to cars carrying children.
The BLF cites worrying research which found that even one cigarette smoked in a car with the windows open was worse than an evening of second-hand smoke in a pub.
Chief executive for the British Lung Foundation, Dame Helena Shovelton, said: "The number of children whose lungs are being damaged by adults lighting up when children are in the car is alarming. Today children across the UK have sent the Government a strong message. The Government can't afford to ignore their plea for protection."
The BLF claims that more than 300,000 children go to their GP with passive smoking-related illnesses each year, whilst figures show that the smoking is related to 9,500 hospital admissions of children annually.