Five of the world's largest carmakers are at the center of a landmark legal battle at London’s High Court, as a sprawling class action lawsuit over alleged diesel emissions cheating gets underway. The trial, which began on October 13, 2025, pits nearly 850,000 claimants against Mercedes-Benz, Ford, Nissan, Renault, and the Stellantis-owned brands Peugeot and Citroen. At stake is not just the reputations of these automotive giants, but potentially billions of pounds in compensation and the future of diesel vehicles in the UK and beyond.
This case marks a decade since the infamous 'dieselgate' scandal first erupted in 2015, when Volkswagen admitted to fitting so-called defeat devices to millions of diesel vehicles. These devices were designed to detect when a car was undergoing emissions testing and temporarily reduce pollution levels, but in real-world driving, emissions soared—sometimes up to 40 times the legal limit for nitrogen dioxide, according to BBC and Sky News. The fallout was enormous: Volkswagen ultimately paid more than £30 billion (over 32 billion euros) in fines, legal costs, and compensation worldwide, with the bulk of settlements occurring in the United States. In the UK, Volkswagen settled with 91,000 owners for £193 million in May 2022, though it did so without admitting liability.
Now, attention has turned to other major automakers. The current trial, described by legal firm Leigh Day as “unprecedented in scale for the legal system in England and Wales,” focuses on a small sample of diesel vehicles from the five manufacturers. However, the implications are much broader. Leigh Day estimates that if the action is expanded—potentially to include up to 1.8 million claimants and 14 car brands, such as Jaguar Land Rover, Toyota, Vauxhall-Opel, and BMW—the total value of the litigation could reach £6 billion. The High Court’s decision is expected to set a precedent, binding hundreds of thousands of similar claims against other manufacturers.
The claimants allege that Mercedes-Benz, Ford, Nissan, Renault, Peugeot, and Citroen used illegal software, or defeat devices, to manipulate emissions tests. According to lawyers representing the motorists, these devices ensured emissions were kept within legal limits during official testing but allowed cars to emit much higher pollution during normal driving. “The vehicles looked less polluting during the testing, but as soon as you were outside the testing regime, those emission levels went massively up,” Martyn Day, a lawyer at Leigh Day, told AFP. He added, “If proven, these allegations would demonstrate one of the most egregious breaches of corporate trust in modern times.”
For many British motorists, the sense of betrayal runs deep. Adam Kamenetzky, one of the claimants, explained to AFP how he felt “defrauded” after buying a Mercedes SUV in 2018, believing it to be less polluting than other models. “We live in a built-up neighbourhood in London where there are children with lungs that can be harmed immeasurably by the emissions that these cars are producing,” he said, highlighting the real-world stakes of the case.
The manufacturers, for their part, strongly deny the allegations. Mercedes-Benz stated its emission control systems were “legally and technically justified,” while Ford dismissed the claims as having “no merit.” Nissan declined to comment, and Renault and Stellantis insisted their vehicles complied with the regulations in place at the time. All five manufacturers reject any comparison to the Volkswagen scandal, arguing that their systems were fundamentally different and that the claims are flawed.
The trial is expected to last three months, with judgment likely to be reserved until mid-2026. Should the court find the carmakers liable, a further trial will be held next year to determine the amount of damages owed to claimants. The outcome will not only affect the five companies in the dock but could also have far-reaching consequences for the wider automotive industry. The court’s ruling will be binding on hundreds of thousands of similar claims against other manufacturers, including Vauxhall/Opel and BMW.
This is not the first time London’s High Court has grappled with the issue of defeat devices. In 2020, the court found that Volkswagen had used such devices to cheat emissions tests, a ruling that paved the way for the 2022 settlement. Since then, the scope of legal action has widened dramatically. The current group of claims, covering 14 manufacturers, is far larger than the VW case, making it one of the largest mass lawsuits in English legal history.
The UK is not alone in pursuing these matters. Courts and regulators around the world have launched investigations into diesel emissions. In July 2025, a Dutch court ruled that diesel cars sold by Stellantis brands Opel, Peugeot-Citroen, and DS contained defeat devices—a decision Stellantis has challenged. Automakers and suppliers have also faced hefty fines and settlements in the United States and elsewhere, as governments crack down on emissions cheating and seek to restore public trust in environmental standards.
For the legal teams and the claimants, the stakes could hardly be higher. Leigh Day says that if the class action is expanded to its full potential, as many as 1.8 million people could be eligible for compensation, and the total cost to the industry could reach £6 billion. “It is a huge case for the British public,” Martyn Day emphasized, adding that it could lead to “serious amounts of compensation.”
As the trial unfolds, the broader questions of corporate responsibility, environmental protection, and consumer trust loom large. The dieselgate saga began as a story of one company’s wrongdoing but has grown into a global reckoning for an entire industry. The outcome of this trial may not only determine the fate of five major carmakers but also shape the future of automotive regulation and accountability in the UK and beyond.
With judgment not expected until mid-2026, the legal and public scrutiny of diesel emissions cheating is set to continue. For now, millions of motorists and industry observers alike are watching closely, waiting to see whether the High Court will deliver a verdict that could reverberate through the automotive world for years to come.