New data suggests worst cars are now 32 times more polluting than the best – risking all diesels being banned from cities, say experts

Ultra-dirty new diesel engines are being sold alongside ultra-clean models in the UK, according to new data, leaving car buyers facing what experts call a “nightmare”.

On-the-road tests by testing firm Emissions Analytics found that new models of Mercedes-Benz CLS, Seat Arona and Citroen DS 7 produced tiny amounts of pollution, up to 75% below the official EU limit.

However, other new diesel models launched in 2017 and 2018 legally pumped out vastly more nitrogen oxide fumes when on the road, having passed a lab-based test. These include a Nissan X-Trail, Ford Kuga and Dacia Duster, with the X-Trail more than 15 times the lab-based official limit.

The discrepancy between the most and least polluting has never been higher, said Nick Molden, CEO of Emissions Analytics, with the worst 10% of cars now 32 times more polluting than the best 10%. “It is a nightmare for car buyers – more of a lottery than it ever has been – and also for city authorities too,” he said.

The dieselgate scandal erupted in 2015, when Volkswagen was exposed as cheating the lab-based emissions tests. But new EU regulations, including a more realistic on-the-road test, are only being phased in slowly. Molden said this is why both clean and dirty models continue to be sold today.

Sales of diesel cars in the UK have plummeted in the last year, which Molden blamed on the failure to ban the dirty models. “Paradoxically, not forcing them from sale is leading to all diesels – clean or dirty – effectively being forced from sale by consumers not buying them,” he said.

Nitrogen dioxide levels are at illegal levels in most urban areas and result in 23,500 premature deaths a year, according to figures from the government, which has been repeatedly beaten in court over the breaches.

Diesel cars produce significantly less carbon dioxide per kilometre than petrol cars and could help curb the rising transport emissions that threaten climate change targets. The cleanest diesel models demonstrate that nitrogen dioxide can be effectively controlled, but Molden said that the simultaneous sale of clean and dirty models could see all of them excluded from city centres: “Policy makers would be forgiven for simply banning all diesels from urban locations.”

'Impossible-to-cheat' emissions tests show almost all new diesels still dirty Read more

Mike Hawes, chief executive of motor industry group SMMT, said new cars passing the latest tests are delivering low emissions on the road and are the cleanest ever. “Thanks to massive manufacturer investment, each generation of vehicle is more advanced than the last,” he said. “All new car models coming to market now meet the world’s strictest and most accurate emissions measurement regime.”

A spokesman for Nissan, which also makes the popular Leaf electric car, said: “All Nissan vehicles fully comply with today’s emissions legislation. We support the more stringent standards that will be implemented later this year and we will be introducing a range of drivetrains to meet them.”

Paul Morozzo, at Greenpeace, said: “Most new diesel cars are still emitting toxic pollution way above the limit. Even if it was possible to clean up diesel it’s a wasted investment as we need a rapid shift to electric vehicles to save the climate.”

The official EU limit for nitrogen oxides is 60mg/km, although car makers have been allowed more than double this until 2019. Emissions Analytics used onboard testing equipment to measure emissions on the road and found very low levels for the Mercedes-Benz CLS (15mg/km), Seat Arona (16mg/km) and Citroen DS 7 (20 mg/km). But the Nissan X-Trail (913mg/km), Ford Kuga (543mg/km) and Dacia Duster (495mg/km) emitted far more on the road.

“It is not enough to know that clean diesels exist, it is necessary to know which are which, model year by model year,” said Molden. Cars’ pollution ratings are given by the free Equa Index website, which uses Emissions Analytics data.