Large "tunnels" covering stretches of motorway to protect locals from dangerous levels of pollution are being considered by Highways England.

The agency said in its latest air quality strategy that it is exploring the possibility of building physical canopies around main roads to soak up car fumes.

In its report, Highways England says it is "investigating if we can reduce the costs to construct a canopy, which is a tunnel-like structure designed to prevent vehicle emissions reaching our neighbours".

After trialling a similar physical barrier to pollution in 2015, which initially stood at four metres high and stretched 100 metres down the M62, the agency said it is now running tests on a material that can clean the air.

If this trial proves successful, the agency said it would consider implementing such barriers across its network of motorways and trunk roads.

Air pollution is linked to around 40,000 premature deaths a year in the UK, and transport also accounts for around a quarter of the country's greenhouse gas emissions.

The agency has been given £100 million by the Government to improve air quality through to 2021, and the strategy released sets out how they plan to spend that money.

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It includes a target to put a charging point for electric cars every 20 miles on 95 per cent of the road network.

The report also said that diesel HGVs are the biggest contributors to roadside levels of nitrogen dioxide, which causes respiratory diseases.

It said: "Emissions from diesel vehicles are a significant contributor to the poor air quality at the roadside."

In its clean air plan, unveiled last month after an order from the courts, the Government set out plans to fund measures to cut pollution with a tax on new diesel vehicles, with an aim to end the sale of all conventional petrol and diesel cars by 2040.