Thousands of cases of asthma, bronchitis and pneumonia linked to air pollution are making the NHS winter crisis worse, doctors are warning.
A group of 175 doctors and health professionals have written to Boris Johnson describing what they call a "public health crisis" with wards and GP surgeries clogged up by patients with respiratory complaints - conditions made worse by poor air quality.
The letter, published in The Times, urges the prime minister to use the Queen's Speech to commit more cash and set a legally binding target to meet World Health Organisation (WHO) guidelines for PM2.5 (particulate matter) pollution by 2030.
The WHO guideline sets an annual mean level of PM2.5 of 10 micro grams/m3.
The medics wrote: "Thousands of children and adults are in hospital or waiting rooms with conditions such as respiratory diseases, bronchitis and pneumonia who would not be there if air pollution was reduced.
"Air pollution isn't just associated with conditions such as lung cancer or asthma, it can also trigger heart attacks, strokes and has been linked with diabetes and depression.
"The hospitals and surgeries we work in are overwhelmed, particularly in A&E, and the severe pressures in the winter months are being exacerbated by preventable causes. This is a public health crisis."
Dr Rob Hughes, senior fellow at the Clean Air Fund, who was among those who signed the letter, said: "As well as properly funding the NHS, it's critical that the new government addresses the root causes of this crisis, including clearing the toxic air which is sending so many people to already busy emergency departments and GP surgeries.
"A new Clean Air Act which adopts the World Health Organisation's recommended limits for pollution would be a good start."
Data from King's College London, which includes figures from nine big UK cities, suggests the risk of emergency hospital admissions for pneumonia in children is on average 2% more pronounced on high pollution days than on lower pollution days.
It also suggests that cutting air pollution by a fifth may result in 4,481 fewer children with acute bronchitis each year in just seven cities.
A government spokesman said: "We are committed to cleaning up our air as well as setting strict new laws on air quality.
"This builds on our £3.5bn plan to improve air quality and reduce harmful emissions, with a Clean Air Strategy, backed by the World Health Organisation as an example for the rest of the world to follow, and our pioneering Clean Air Zones delivering urgent action to clean up our air.
"To deliver a world-class health care system, we are providing the NHS a record cash funding boost worth an extra £33.9bn a year by 2023-24."