The study measured 2015 NO2 levels in the air at 110 monitoring stations across the UK, some by the roadside, others at background locations or in rural areas.

The European Union sets NO2 levels at 40ug/m3 (micrograms per cubic metre) on average over a year. However, a total of 18 stations were found to be this level, including in areas such as Camden, Oxford centre and Glasgow.

John McClean, GMB national health, safety and environment officer, said: "These figures on nitrogen dioxide confirm the urgent need for better air quality monitoring in urban and built up areas. Clean air should be a right, not a privilege.

“Road transport is a major cause of air pollution. Even though engine technology is improving, these exposure levels are still dangerously high, and place workers and the public at increased risk of respiratory diseases.”

He added: “We reiterate our call for high polluting vehicles to be banned from city centres, and for local authorities to take immediate action in priority areas such as near schools, hospitals and GP surgeries.

“Waiting for technology to reduce emissions is not an acceptable response. GMB calls for action now.”