More diesel cars and vans are appearing on Calderdale’s roads, despite the dangerous pollutants many emit.
The Government aims to end sales of new conventional petrol and diesel cars by 2040 as part of efforts to clean up transport.
In Calderdale, there were 36,194 registered diesel cars by the end of 2018, and 10,889 diesel vans.
They made up 43 per cent of the area’s vehicles, while around one in every 330 were ultra low emissions vehicles - an electric or plug-in hybrid car.
Across the UK, 43 per cent of all vehicles are diesel and one in 200 are ULEVs.
Steve Gooding, director of the RAC Foundation, said: "These figures show there remains a gaping hole between the ambition to green the vehicle fleet and the reality on the road.
"The relatively slow take up of electric cars shows how important government incentives remain.
"The data also underlines the continued dominance of diesel. Whilst there are more petrol cars than diesel, diesel fuel sells at almost twice the volume because of its use in almost all commercial vehicles including HGVs and the fast-rising number of vans."
The number of diesel cars and vans in Calderdale has increased by 10 per cent since 2015, when the environmental impact was highlighted after Volkswagen was caught cheating emissions tests. That’s 4,100 more diesel cars and vans on the streets.
Nick Molden, chief executive of Emissions Analytics, an emissions testing company, explained: “Diesel cars give off less carbon dioxide per mile than petrol cars.
"That was the reason for promoting them in the first place.
"After the Volkswagen scandal people became aware of the nitrogen oxides problem, which diesel cars inherently have, and require the correct exhaust treatment system to contain."
Mr Molden explained new diesel cars can be more environmentally friendly than petrol cars, as the latest technology stops the nitrogen oxide emissions, while giving off less carbon dioxide.
However, he estimated that only 10 per cent to 15 per cent of diesel cars on the road today produce acceptable levels of nitrogen oxides.
An ultra low emissions zone has been introduced in London, in which older diesel cars and some petrol cars will have to pay £12.50 to enter.
Mr Molden described it as one of the “most advanced low emissions systems in the world”, however he urged local authorities looking to improve air quality to base access on real-world emissions ratings, rather than lab-tested Euro standards.