In most countries, air pollution is still one of the biggest threats to people's health. In London, things have been getting better - and that's largely down to tougher transport rules.
An independent analysis by experts from Imperial College London found that the Ultra Low Emission Zone (ULEZ), which keeps the most polluting vehicles off the road, has cut levels of fine particle pollution (PM 2.5) by 31 per cent in outer London and nitrogen dioxide, the traffic-linked gas that irritates the lungs, by 27 per cent across the city.
