Which? says most cars break EU pollution laws
A majority of cars break European pollution laws when they're driven on the road, according to data from Which?
The consumer rights group has compiled more than 300 car checks since 2012.
They all passed the European emissions laboratory test, but on the road 95% of the diesels and 10% of the petrol cars produced more nitrogen oxides than the legal limit.
Manufacturers only have to pass the official lab test before they can sell their cars.
Nitrogen oxides are a family of poisonous, highly reactive gases.
Which? also found that 65% of petrol cars produced more carbon monoxide than the 2006 limit.
It said 38 of the cars tested wouldn't pass the emissions limit set by the EU in 1993.
Fit for purpose?
Which? executive director Richard Lloyd, said, "Car emissions and fuel claims are important factors when buying a new car, so drivers will be shocked by the results of our testing.
"The current official tests are clearly not fit-for-purpose and we urgently need a new regime put in place that reflects the reality of how we drive."
Plans are underway to ensure that by 2017 official EU tests reflect the real conditions found on the road.
Which? is among many campaigners pressing for the changes to be made sooner.
It's not the first time that data has shown how much more polluting cars are on the road compared to the testing lab.
The car industry is open about the problem.
It blames the European testing system which it says is formulaic and doesn't reflect the way humans drive.
There are no hills in the laboratory test or turns, while acceleration and gear changes are gentle.
A recent Panorama programme on the VW emissions scandal revealed how the tests work.
It's estimated that 29,000 people die from air pollution in the UK every year - more than obesity and alcohol combined - and that's just for one type of pollutant.
A six year study testing thousands of children living in East London also suggested air pollution is stunting the growth of their lungs by as much as 10% and making them more prone to disease.
It backs up a similar study in California.
Other research is looking at whether pollution increases the risk of brain damage and strokes.
The European Commission has launched legal action against the British government because it has failed to meet its nitrogen dioxide targets in the vast majority of the 43 zones where pollution is measured.
Last year, VW admitted cheating emissions tests in America to make its vehicles look greener, but no other car company has been found to be rigging its engines.
In the light of the VW scandal, a number of governments including those in Britain, France and Germany are randomly testing cars to see what they're emitting.
In France, a commission set up to check 100 different vehicles told Renault to recall 15,000 cars because they were deemed to be excessively polluting when they were too hot or too cold.
The French government was keen to stress that Renault had not been using software designed to cheat official tests.
Also two other non-French car makers that they checked had a similar issue.
You can follow Richard on Twitter @BBCwestcott