Most modern diesels still too dirty, study shows

Some diesel cars produce more than 25 times the legal limit for oxides of nitrogen, according to a consumer group.

Tests commissioned by Which? since the beginning of last year found that 47 out of 61 diesel car models exceed the latest Euro 6 limit for NOx, despite conforming to official standards.

The worst of those looked at was the Subaru Forester, which emitted more than 25 times the legal limit, the research found.

Which? managing director of home products and services Alex Neill said: "The current official tests fail to measure the actual level of emissions that cars are producing on our roads.

"Most diesels we assess are producing far more NOx in our tests than official limits allow.

"The new official tests should help reduce harmful emissions - but we will continue to penalise any car we find that produces excessive levels of pollutants in our tests."

Since September last year, new models have had to pass tougher tests.

These include laboratory exams and being monitored while on the open road.

Mike Hawes, chief executive of industry body the Society of Motor Manufacturers and Traders, said: "The non-official test employed by Which? is very different from the current EU test, so it's no surprise it delivers different results.

"Only the official tests accurately compare models on a like-for-like basis, helping inform consumers.

"The differences between lab and on-the-road performance are well known and the new, much stricter WLTP lab test, together with the real world RDE test, will help assure motorists that new cars on sale today are the cleanest in history.

"Indeed, no new car model can be sold in the UK unless it meets this new, robust standard."