Air pollution could rise significantly as coronavirus restrictions end, a think tank warned as it called on cities to reboot stalled plans to tackle the problem.
Levels of toxic air fell dramatically in many places in the spring as the country went into full lockdown, Centre for Cities said.
But analysis shows that concentrations of air pollution have risen again over the summer to pre-pandemic levels or higher, even though most of the country remains under restrictions.
This means that, as life returns to normal, pollution could climb even higher, the think tank warned.
It is calling for councils which shelved their pollution reduction plans in the face of the pandemic to revisit them.
Pollution, such as nitrogen dioxide from traffic, is linked to 40,000 deaths a year in the UK, and research has suggested that 15% of Covid-19 deaths can be attributed to toxic air.
Concentrations of nitrogen dioxide fell on average by 38% in cities and large towns as a result of lockdown, analysis from Centre for Cities in partnership with the Centre for Research on Energy and Clean Air (Crea) said.
Some of the biggest falls were seen in Glasgow, with a 57% reduction, followed by Warrington and Oxford, where pollution levels also more than halved, though other places such as Southampton saw much smaller drops.
But nitrogen dioxide emissions bounced back in most cities as the first national lockdown eased and cars and traffic returned to the roads.
In four-fifths of cities and larger towns pollution levels were back to at least pre-lockdown levels by September, despite economic activity not having fully recovered by then, according to the analysis based on official data.
In some places, such as Barnsley, Bournemouth and Portsmouth, nitrogen dioxide levels by September were already even higher than they were before the spring lockdown.
Centre for Cities said a number of councils were scheduled to launch clean air zones, which charge vehicles with higher levels of emissions to drive through certain areas to combat pollution.
But many plans have been delayed or even scrapped amid claims they were not immediately necessary because air quality had swiftly improved in 2020, the report said.
Centre for Cities argues that is not the case, with pollution rising as private cars have returned to the roads while public transport use remains low.
And an increase in working from home will not curb pollution, the organisation said, warning that in places such as London commuting is not the biggest cause of pollution and remote workers are more likely to use their cars for leisure.
It is calling for councils and mayors to discourage car use by introducing clean air zones, improve buses, rail and tram systems to encourage use of public transport, and put in measures to boost cycling and walking.
Centre for Cities’ chief executive Andrew Carter said: “Toxic air has contributed to the deaths of thousands of Covid-19 victims this year and, even after the pandemic ends, will remain a big threat to health – particularly for those living in urban areas.
“City leaders can reduce threat of air pollution, but it will take political will.
“Discouraging car usage will be unpopular in the short term but, if coupled with the necessary improvements to public transport, the long-term benefits to public health and the economy will be huge and our cities will become better places to live.
“Now is not the time for politicians to delay on this.”