Investors will shun capital if it fails on toxic air, warns Bloomberg

12-year stint as mayor of New York, when he rolled out an acclaimed climate-change action plan. To meet his pledge of making New York the cleanest large city in America, he invested in more than 100 clean air monitors at street level. He said he wants to see far more on the streets of London.

His message came as the Government was forced to publish its clean air plan before the election by the High Court. The Department for Environment, Food and Rural Affairs had been accused of trying to delay publication of the strategy, which is thought to involve a number of penalties for drivers.

He said: “What we learned was startling: one per cent of the city’s buildings — the ones that used the dirtiest heating oils — were producing more soot pollution (PM 2.5) than all the vehicles on our roads combined.

“Armed with that information, we were able to build public support for banning the dirtiest-burning heating oil, requiring energy audits in large buildings, and incentivising investments in cleaner energy.”

New York’s air quality rose to its cleanest level in 50 years, and increased life expectancy by three years during his time as mayor. To help cities around the world get to grips with air quality monitoring, his company Bloomberg Philanthropies will open a London office later this year. He wants to arm citizens with knowledge of emissions at street level.