The dieselgate scandal first emerged in September 2015, when the US Environmental Protection Agency accused Volkswagen of installing software – known as “defeat devices” – on diesel cars to lower readings of the cars’ nitrogen oxide emissions.
This software recognised when cars were undergoing official emissions tests, and turned on systems designed to reduce their output of nitrogen dioxide, a gas which can cause respiratory problems.
But when the cars were used on the road, the systems were turned off, in order to improve performance. The net result was that cars produced significantly higher levels of pollution in everyday use than official figures suggested.
VW later admitted the defeat devices had been used deliberately to circumvent emissions tests in the US, and had been fitted to some 11 million cars worldwide. It paid out some £26bn in fines and compensation.
Lawyers say this case is the largest class action in English and Welsh legal history, and could eventually involve 1.6 million car owners.
The five companies were chosen by the court as lead defendants to be tried first as the case is so big. They have been accused by 220,000 car owners of misleading them over emissions tests.
But depending on the outcome of this case, nine other carmakers are facing similar claims.
In 2020, the High Court ruled that Volkswagen had used defeat devices in breach of European Union rules to pass emissions tests.
Volkswagen settled a class action out of court, paying £193m to 91,000 British motorists.
The company has so far paid out more than €32bn (£27.8bn) over the scandal, mostly in the US.
Gathered outside the High Court on Monday were campaign group Mums for Lungs, and Rosamund Adoo-Kissi-Debrah, whose nine-year-old daughter Ella was the first person in the UK to have to have air pollution listed as a cause of death when she passed away in 2013.
