A study has found children are at greater risk of dangerous levels of air pollution when traveling inside a car than when outside a vehicle.
Writing for the Guardian, professor Sir David King has found that walking to school or cycling is actually better for children than being driven to school, as they are exposed to less pollutants.
He said: "Children sitting in the backseat of vehicles are likely to be exposed to dangerous levels of air pollution.
"You may be driving a cleaner vehicle but your children are sitting in a box collecting toxic gases from all the vehicles around you."
He also argues that although legislation has now been introduced banning smoking in cars with children, they are still breathing in toxic emissions from such vehicles when sat inside them.
Experiments dating back as far as 2001 show drivers breathe in much higher levels of toxins than people cycling or walking. So for children who have no choice when sitting in the rear of a car, it is a major concern.
Professor Stephen Holgate is an asthma expert from the University of Southampton. He spoke to the guardian about pollutant levels, saying: "It is nine to 12 times higher inside the car than outside.
"Children are in the back of the car and often the car has the fans on, just sucking the fresh exhaust coming out of the car or lorry in front of them straight into the back of the car."
Another issue the experts point out is the level of nitrogen dioxide in diesel vehicles, which have been above legal limits in almost 90 per cent of urban areas throughout the UK for more than seven years.
Holgate added: "Air pollution hasn't been taken seriously. There is a very strange situation where the government has to make laws by being taken to court repeatedly.
"In my view it is really quite appalling that we haven't started to deal with this properly and put children's and adults' health first."