Research by the Royal College of Physicians has found that more than 800 children visit their doctor every day suffering from the serious effects of breathing in second-hand smoke.
The Government has launched a new campaign on the back of the alarming statistics to increase awareness of the hidden dangers to children of smoking in homes and cars.
The Royal College of Physicians found that more than 80% of second-hand smoke is invisible, odourless and contains harmful cancer-causing toxins and poisons.
Sky News reports that new TV adverts will show how leaning out of a car window or the back door to puff on a cigarette is not enough to protect children from the risks.
Professor Dame Sally Davies, the Chief Medical Officer, told Sky: "It's well known that smoking kills, but many smokers still don't realise the damage their smoke causes to those around them.
"Second-hand smoke can be an invisible killer and with more than 300,000 children seeing their GP each year because of it, we need to make sure people know how dangerous it can be."
A survey of nearly 700 parents undertaken this month found that 68 per cent admitted to smoking in the car with their children present.
Dr Harpal Kumar, CEO of Cancer Research UK said that the 'evidence is clear' that children are at risk from second-hand smoke.
"Smoking around children is harmful. It's vital they are protected from the dangers of second-hand smoke," Dr Kumar said.
The NHS has set up a website, smokefree, to help smokers kick the habit.