The High Court will decide whether systems installed in Mercedes, Ford, Peugeot-Citroen, Renault and Nissan diesel vehicles were designed to cheat clean air laws.

The five lead defendants deny the accusations.

The huge trial will have ramifications for other manufacturers, potentially paving the way for "billions of pounds" in compensation, said Martyn Day, lawyer at Leigh Day representing the claimants.

The dieselgate scandal first erupted in September 2015, when German automaker Volkswagen was found to have cheated pollution tests by installing so-called defeat devices to reduce nitrogen oxide readings.

It caused waves in the global car industry, ensnaring several other top carmakers and leading to legal action in several countries.

The new trial, scheduled to last three months, comes after 1.8 million UK drivers brought complaints against the five lead defendants, as well as other manufacturers like Jaguar Land Rover, Toyota, Vauxhall-Opel and BMW.

"It's much wider than VW (Volkswagen), it's for nearly all the manufacturers in this country," Day told AFP.

Although not all the carmakers are directly part of the trial, they could still be required to pay compensation depending on the judge's ruling.

- UK compensation -

Adam Kamenetzky, one of the claimants, bought a Mercedes SUV in 2018 on the belief that it was less polluting than other models.

He told AFP that after he had "paid a premium for what was supposed to be a green SUV, it turned out to be an absolute lie."

But for claimants like Kamenetzky, it will take some time for any possible compensation to reach them.

The trial beginning on Monday must first determine whether carmakers are liable, before a separate compensation phase can follow next year.

German automaker Mercedes told AFP that emissions control software was based on technical needs, not an attempt to cheat regulatory tests.

These mechanisms were "justifiable from a technical and legal standpoint," a spokesperson said.

Mercedes and US carmaker Ford both rejected the claims as having "no merit," while Japan's Nissan declined to comment.

French manufacturers Renault and Stellantis, parent of Peugeot and Citroen, both said the vehicles they sold were compliant with regulation at the time.

The High Court in 2020 found 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 193 million pounds ($259 million) to 91,000 British motorists.

To date, Volkswagen has had to pay more than 32 billion euros worth ($37 billion) in penalties over the scandal, mostly in the United States.

ajb/jkb/gv

Mercedes-Benz Group

Ford Motor Company

Groupe PSA

Renault

Nissan Motor

Volkswagen

Jaguar Land Rover

TOYOTA MOTOR

BAYERISCHE MOTOREN WERKE AG

Stellantis