High levels of imported pollution from mainland Europe are behind Sadiq Khan’s decision to trigger a “high pollution” alert for the first time in almost two years.

The Mayor of London issued the warning on Tuesday until the end of Thursday amid “extremely dangerous” toxic air from the continent alongside a build-up of local emissions.

He has urged Londoners to “look after each other” by choosing to walk, cycle or take public transport to work or school, and has advised people with heart and lung problems to avoid physical exertion.