Ministers want to end sales of conventional petrol and diesel cars by 2040 in a move they insist will clean up transport and reduce pollution.
But last year in the West Midlands nearly 900,000 diesel vehicles were registered, including 649,780 cars and 239,229 vans.
They made up half of the area’s vehicles on the road, while only around one in every 90 vehicles were ultra low emission (ULEV), such as electric or plug-in hybrid cars.
Since 2015 the number of diesel cars and vans in the West Midlands has increased by eight per cent – an extra 69,100 on the roads.
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.”
Diesel fuel has become a contentious issue in recent years.
Its environmental impact was highlighted after Volkswagen was caught cheating on emissions tests in 2015, but critics argue the fuel’s negative impact has been overstated.
Nick Molden, chief executive of Emissions Analytics, an emissions testing company, said: “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 said new diesel cars could 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 10-15 per cent of diesel cars on the road today produce acceptable levels of nitrogen oxides.
An ultra low emissions zone is being introduced in Birmingham from January next year, in which older diesel cars and some petrol cars will have to pay £8 to enter. A similar scheme was introduced in London this month.