The High Court, where the trial opened in October, will determine whether systems installed in Mercedes, Ford, Peugeot-Citroen, Renault and Nissan diesel vehicles were designed to cheat clean-air laws.

Lawyers will present their closing arguments in the trial's latest phase, expected to last three weeks, with a final decision in the summer.

- 'Staggeringly expensive' -

It could lead to a second trial and billions of pounds in compensation.

The five lead defendants deny that their systems were designed to circumvent the tests.

"The claimants commenced this staggeringly expensive litigation without a coherent, formulated position founded upon solid expert evidence," Renault said in its closing submissions sent to AFP.

Speaking outside court on Monday, Jemima Hartshorn, founder and director of campaign group Mums for Lungs said:

"The real crux of the case is really that there is still millions of these cars on our roads that are emitting really high levels of toxic nitrogen dioxide which is making our children sick and car manufacturers are responsible."

The dieselgate scandal erupted in September 2015, when German automaker Volkswagen admitted to fitting millions of vehicles with software to make engines appear less polluting in regulatory tests than in real driving conditions.

It caused waves in the global car industry, ensnaring several other top carmakers and leading to legal action in multiple countries including France, South Korea and the United States.

- Compensation claims -

When the High Court in 2020 found Volkswagen had used defeat devices to cheat emissions tests, the German automaker settled out of court, paying pound193 million ($259 million) to 91,000 British motorists.

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

Claims in the ongoing trial were brought on behalf of 1.6 million motorists against 14 carmakers, including Jaguar Land Rover, Toyota, Vauxhall-Opel and BMW, among others.

The outcome of the five lead defendants' trial could set a precedent for compensation claims against other manufacturers involved.

Contacted by AFP, Ford and Mercedes again rejected the claims as having "no merit", while the other manufacturers did not wish to issue a new statement or did not respond.

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

Nissan declined to comment.

A possible second set of proceedings later this year would address compensation.

bur-ode/bcp/ajb/rlp

Mercedes-Benz Group

Ford Motor Company

Groupe PSA

Renault

Nissan Motor

Volkswagen

Jaguar Land Rover

TOYOTA MOTOR

BAYERISCHE MOTOREN WERKE AG

Stellantis