There are 47 towns and cities in the UK which match or exceed air pollution limits, a report has revealed.
The World Health Organisation (WHO) said the Welsh steel town of Port Talbot is the most polluted place in Britain.
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It recorded pollution levels of 18 micrograms per cubic metre, well above the WHO limit of 10.
Researchers looked at fine particle emissions – called PM 2.5 – which travel deeply into people’s respiratory systems and can lead to health problems.
The tiny particles, which come from sources such as transport, industry, coal plants and burning wood, fuels or waste, are linked to conditions including stroke, heart disease, lung cancer and disease, and respiratory infections.
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Many of the country’s main cities exceed the WHO limit, including London, Manchester, Liverpool and Nottingham.
Port Talbot, home of the Port Talbot steelworks, recorded 18 micrograms per cubic metre in the last recorded data from 2015, the same as Marseille in France, Singapore and the Ecuadorian capital Quito, and higher than Belgian capital Brussels (16).
The figures show varying levels of pollution in Port Talbot over time, with the figure at 16 in 2013, down to 10 in 2014 and on the rise again in 2015.
Scunthorpe and Salford recorded the second-worst levels of pollution in the UK, with 15 micrograms per cubic metre recorded, followed by Gibraltar and Thurrock on 14.
Manchester and Swansea were on 13, and cities including Leeds, Leicester, Liverpool, Plymouth, Sheffield and York recorded 12, one above London which showed 11 micrograms per cubic metre in 2015.
This figure represents a drop from 17 in 2013, while in Carlisle the levels have gone up from eight in 2013 to 12 in 2015.
Cities on the WHO limit of 10 include Birmingham, Brighton, Bristol, Newcastle, Portsmouth and Southampton.
The most polluted city in 2015 according to the WHO data is Muzaffarpur in India, with a figure of 197 micrograms per cubic metre, although this figure is under revision.
Below that is Pasakha in Bhutan (150), Delhi in India (123) and greater Cairo in Egypt (117).
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The government has been urged to take action in the wake of the report, which said seven million people a year worldwide are dying due to poor air quality, and nine out of 10 people are exposed to levels of air pollution that are dangerous to their health.
Environmental law charity ClientEarth chief executive James Thornton said: “These new statistics show a worrying level of this dangerous air pollution across the country.
“People shouldn’t have to breathe air on a daily basis which the WHO deems unhealthy.”
He added ministers should commit to a new Clean Air Act, adding: “Without it, many people across the UK will continue to pay with their health.”
Alison Cook, director of policy at the British Lung Foundation, said: “This report reconfirms that air pollution is one of the leading environmental public health crises in the UK today.
“Action to reduce the toxic particles in the air we breathe can no longer be delayed.
“How much more evidence do we need to see before the Government sets new legal limits on pollution levels to protect the nation’s lung health?”
Simon Gillespie, chief executive of the British Heart Foundation, said: “The UK government needs to show leadership by adopting WHO air quality guidelines into national legislation and in doing so, help to protect the nation’s heart and circulatory health.”
