One year after the Volkswagen "dieselgate" scandal, nearly 30 million cars on Europe's roads are still way over air pollution limits, campaign group Transport and Environment said in a report Monday.

The German car manufacturer admitted in September 2015 to installing so-called "defeat devices" in 11 million diesel cars that enabled them to pass emissions tests they would otherwise have failed. 

Greg Archer, the clean vehicle director at the Brussels-based NGO, said "one year after the US caught Volkswagen cheating, all carmakers keep selling grossly polluting diesel cars with the connivance of European governments."

The study found that not one brand complied with current air pollution limits in real-world driving conditions, with Fiat and Suzuki diesel cars spewing out 15 times more nitrogen oxide than the current legal limit.

Nitrogen oxide is linked to respiratory and cardiovascular diseases. The European Environment Agency said in a 2015 report that nitrogen oxide was responsible for around 72,000 premature deaths in Europe.

Volkswagen Euro 6 cars -- cars sold after 2015 in line with the latest EU emission standards -- were the least polluting but still belched out nearly twice as much as the official standard. 

Four out of every five Euro 5 standard cars -- sold between 2010 and 2014 -- failed to meet those limits, producing on average three times the ceiling.

The study used emissions tests data from around 230 diesel cars gathered in tests by the British, French and Italian governments and public databases.

France was the country with the most "dirty" cars on the road, with 5.5 million not reaching standards, followed by Germany on 5.3 million, Britain 4.3 million and Italy 3.1 million.

The NGO urged a recall of all harmful diesel cars and the institution of a European watchdog "to stop EU member states protecting their national champions and to ensure the single market for vehicles operates in the interests of all citizens."