The vast majority of the world’s children are breathing air so polluted that it puts their health and development at serious risk, a World Health Organization report has warned.

Over 90 per cent of all children - roughly 1.8 billion - live in places where pollution exceeds WHO guidelines. Ambient air pollution caused roughly 4.2 million premature deaths in 2016, while 600,000 children died from acute lower respiratory infections due to dirty air.

The problem is most pronounced in low and middle income countries, where 98 per cent of children under five breath toxic air every day. The consequences are life-long; exposure to pollution is linked to asthma, childhood cancer and reduced neurodevelopment and cognitive ability.

Those who live in highly polluted areas at a young age - when their lungs, organs and brains are still maturing - may also be at a greater risk of developing chronic diseases, including obesity, later in life.

But the impacts of pollution start before birth, with woman who are exposed during pregnancies more likely to have a premature birth or low-weight baby.