High levels of pollution are being emitted by diesel vehicles built by a range of car makers other than Volkswagen, it has been reported.
New diesel cars from manufacturers including Renault, Nissan, Hyundai, Citroen, Fiat, Volvo allegedly produce more emissions when tested in realistic driving conditions, according to data from Europe's biggest motoring organisation.
Only a quarter of the 79 different cars tested by Adac matched their official performance on the existing EU test, it has been reported in the Guardian and Independent newspapers.
The results show the Volvo S60, Renault's Espace Energy, the Jeep Renegade and Nissan-made X-Trail all exceeded legal European limits for nitrogen oxide (NOx) by more than 10 times.
Reinhard Kolke, head of test and technical affairs at Adac, told the Guardian: "If all cars complied with [the official EU NOx limit], we would have solved all the worst health effects.
"Every consumer has the right to expect all manufacturers to do this. But still there are these gross emitters."
Adac put the diesel models through the EU's existing test (NEDC) then compared the results with a longer UN-sanctioned test (WLTC) which is believed to represent more realistic driving conditions.
A Nissan spokeswoman said: "We can state unequivocally that we are committed to upholding the law and meeting regulations in all markets."
A Renault Group spokesman said: "The group complies with all regulations and legislation for the markets in which it operates. Its vehicles are not equipped with defeat devices."
"Hyundai Motor abides by the testing regulations and methods of each region where it sells cars including Europe," said a spokeswoman.
Citroen, Fiat and Jeep have not commented on the findings.
There is no suggestion any of the other manufacturers used devices to cheat the testing process.
The revelations come after it was announced that nearly one in 10 diesel cars in the UK are fitted with the software that caused the Volkswagen scandal.
VW confirmed that nearly 1.2 million UK vehicles are affected, consisting of 508,276 Volkswagen cars, 393,450 Audis, 131,569 Skodas, 79,838 VW commercial vehicles and 76,773 Seats.
The German car-maker said it would contact the owners to arrange for their vehicles to be "corrected".
The scandal began in the US, where the Environmental Protection Agency said 482,000 Volkswagen vehicles were fitted with sophisticated defeat device software, which switches engines to a cleaner mode when they are undergoing official testing.
Once on the road the cars produced nitrogen oxide pollutants at up to 40 times the legal standard.
VW has admitted that 11 million of its diesel vehicles worldwide were fitted with the software.
The company said that just over 1.1 million UK cars are affected, which is 9.9% of the country's diesel cars. Latest figures show that 11.2 million are licensed for use on UK roads.