City leaders across England and Wales have teamed up to demand that Theresa May take immediate action to fight air pollution, which scientists say causes at least 40,000 premature deaths a year in the UK.

A total of 17 mayors and civic leaders, representing 20 million people throughout the country, have signed a letter that calls for a national action plan to clean up the nation’s air to be implemented as a matter of urgency. They include the London mayor, Sadiq Khan, as well as mayors Andy Burnham (Greater Manchester), Steve Rotheram (Liverpool city region), and Dan Jarvis (Sheffield), along with leaders from authorities around the country including Cardiff, Leeds, Newcastle and Southampton.

“Our country’s polluted air is shortening lives, damaging our children’s lungs, and severely impacting on the NHS as well as costing the economy in working days lost,” they say. “Crucially, these consequences ... disproportionately affect the poorest and most vulnerable.”

The group is demanding that the government:

• Pass a stringent clean air act that will give local authorities powers to regulate emissions such as those produced by taxis and private hire services in cities.

• Set up a targeted vehicle renewal scheme to replace older, more polluting cars, buses and lorries, but in a way that will protect local businesses.

• Provide funds to support the establishment of clean air zones and provide investment in cleaner buses, taxis and other forms of transport.

The letter, also sent to the chancellor, Philip Hammond, and the environment secretary, Michael Gove, was written in the wake of the national clean air summit in June when many civic leaders met to debate the air pollution crisis. The event was jointly hosted by the mayor of London, the UK100 cities network and the Institute for Public Policy Research.

“Our most deprived communities, who already have to cope with multiple health problems, suffer most from the effects of polluted air,” said Rotheram. “In Liverpool we have areas where men have a life expectancy seven years lower than the national average. There is only so much that we can do as an individual area, which is why we need a national plan for clean air.”

This view was backed by Bristol’s mayor, Marvin Rees. “It is unacceptable that lives are at risk,” he said. “We need the government to show leadership with a way to support low-income, vulnerable families and small businesses who rely on diesel vehicles to be able to shift to cleaner cars.”