The nitrogen dioxide emitted by vehicle exhausts, particularly from diesel engines, can reduce attention and reaction times in drivers.

This is the view of researchers at the London School of Economics who have found a link between pollution and road accidents, and say that reducing nitrogen dioxide levels by one third in badly-polluted West London could reduce accidents by 5%.

One major contributor to UK pollution, Volkswagen, have still to modify a million of their cars fitted with software to cheat emission tests, a process they promised would be completed by the end of this year.