The class action beginning at the High Court today could yet be expanded to include 1.8 million customers of 14 car brands, one law firm involved in the case says.

Five major car brands have gone on trial in the UK over so-called dieselgate.

The class action lawsuit, involving 850,000 drivers, is being heard at the High Court.

It's been 10 years since dieselgate first came to light.

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That was the scandal which engulfed the Volkswagen group, later costing the company around £30bn in fines and compensation.

It was revealed in 2015 that the German carmaker had fitted so-called defeat devices to most diesel models - software that would give a false, low, reading when the vehicles were undergoing emissions testing.

The bulk of VW's bill was paid out in the United States where it was claimed that vehicles were emitting up to 40 times the legal limit of nitrogen dioxide when out on the road.

Here in the UK, Volkswagen settled claims for a £193m total payout to 91,000 owners in May 2022.

The next stage of dieselgate-related legal action expected to last three months at the High Court, with judgment tipped to be reserved to a later date in mid 2026.

Owners of diesel vehicles made by Mercedes-Benz, Ford, Nissan, Renault, Peugeot and Citroen claim the companies, like VW, used unlawful software to ensure emissions were kept within legal limits during testing.

They argue those limits were far exceeded during normal on-the-road use.

The case will focus on a small sample of diesel vehicles produced by the five manufacturers.

One of the lead solicitors' firms handling the claims, Leigh Day, says the class action is unprecedented in scale for the legal system in England and Wales and could eventually take in up to 1.8 million people if expanded in future to the 14 brands it believes cheated testing regimes.

The law firm says in that event, the case could be worth up to £6bn.

Dieselgate: Five carmakers go on trial in UK