On Monday, October 13, 2025, the imposing halls of London’s High Court became the stage for a legal showdown that could reshape the auto industry across Europe—and perhaps the world. Five of the globe’s leading carmakers—Mercedes-Benz, Ford, Nissan, Renault, and Stellantis-owned Peugeot and Citroën—are in the dock, accused by a staggering 1.6 million claimants of cheating diesel emissions tests. This case, already dubbed the largest class action in English and Welsh legal history, is the latest—and perhaps most consequential—chapter in the saga known as "dieselgate."
The roots of this scandal reach back a decade. In September 2015, the U.S. Environmental Protection Agency (EPA) revealed that Volkswagen had installed so-called "defeat devices" in millions of its vehicles. These devices made engines appear less polluting during regulatory tests than they actually were on the open road. The fallout was immense: Volkswagen has since paid over €32 billion (roughly £27.8 billion) in fines, compensation, and vehicle buy-back programs worldwide, with a record A$125 million paid to the Australian government alone, according to CarExpert. Volkswagen also slashed diesel offerings in its passenger car lineup, leaving only a handful of commercial models on the market.
Now, a decade later, the focus has shifted to other major players. According to BBC, the five carmakers currently on trial were selected as lead defendants due to the sheer scale of the allegations. The court’s decision could set a precedent for nine additional automakers, including Jaguar Land Rover, Toyota, Vauxhall-Opel, and BMW, who may face similar claims depending on the outcome. The full scope of the litigation encompasses 14 manufacturers and is valued at approximately £6 billion ($7.97 billion), as reported by Reuters.
The crux of the claim is both simple and damning. Claimants allege that these manufacturers installed unlawful defeat devices—software that could detect when a vehicle was undergoing emissions testing and temporarily reduce engine performance to keep emissions within legal limits. Once the vehicle was back on the road, the software would allow the engine to run at normal power, causing nitrogen oxide emissions to spike well above regulatory thresholds. As lawyer Martyn Day of Leigh Day, one of the 22 law firms representing the claimants, put it to BBC: "A decade after the Dieselgate scandal first came to light, 1.6 million UK motorists now get their chance to establish at trial whether their vehicles contained technology designed to cheat emissions tests."
Day didn’t mince words regarding the potential impact. If the allegations are upheld, he said, it "would demonstrate one of the most egregious breaches of corporate trust in modern times." He added, "It would also mean that people across the UK have been breathing in far more harmful emissions from these vehicles than they were told about, potentially putting the health of millions at risk." Day echoed similar sentiments in an interview with AFP, highlighting the case’s broad implications: "It is a huge case for the British public," he said. "It could lead to serious amounts of compensation."
For many affected owners, the sense of betrayal runs deep. Adam Kamenetzky, a claimant who bought a Mercedes SUV in 2018, told AFP he felt "defrauded." He explained, "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." The trial, which is expected to run for three months, will first determine whether the carmakers are liable. If the court finds against them, a separate trial to decide compensation is scheduled for autumn 2026. But a final judgment isn’t expected until summer 2026, meaning claimants like Kamenetzky may have to wait a while for any potential payout.
The manufacturers, for their part, have vigorously denied any wrongdoing. Mercedes-Benz insists its "emission control systems were legally and technically justified." Renault and Stellantis, parent company of Peugeot and Citroën, maintain that their vehicles were compliant with regulations at the time. Ford has dismissed the claims as having "no merit," while Nissan has stated its commitment to compliance in all markets, declining further comment. All five companies reject any comparison to the original Volkswagen dieselgate scandal, arguing that the claims against them are fundamentally flawed.
The High Court trial will focus on a small, representative sample of diesel vehicles produced by the five manufacturers. The outcome will be binding not only for these companies but also for hundreds of thousands of similar claims against other manufacturers, such as Vauxhall/Opel and BMW. As Reuters notes, this is not the first time London’s High Court has ruled on defeat devices. In 2020, it found Volkswagen guilty of using such devices in breach of European Union rules. Volkswagen settled those claims out of court in 2022, paying £193 million to 91,000 British motorists, but without admitting liability.
The legal reverberations of dieselgate have been felt far beyond the UK. Automakers have faced lawsuits in the Netherlands, where a court recently ruled that diesel cars sold by Stellantis brands Opel, Peugeot-Citroën, and DS contained defeat devices—a decision Stellantis has contested. In the United States, manufacturers and suppliers have paid substantial fines and reached settlements to resolve investigations into diesel vehicle emissions.
So, what’s at stake here? Billions of pounds in compensation, certainly, but also the trust of millions of motorists and the reputation of an industry already battered by environmental scandals. As Martyn Day emphasized to BBC, "If the allegations are upheld in court, it would demonstrate one of the most egregious breaches of corporate trust in modern times." The companies’ steadfast denials, however, set the stage for a protracted and fiercely contested legal battle.
Outside the courtroom, the trial has reignited broader debates about air quality, public health, and the accountability of powerful corporations. As the world continues to grapple with the environmental and human costs of diesel pollution, the outcome of this trial could signal a turning point—not just for the carmakers in the dock, but for the entire automotive sector. For now, all eyes are on London’s High Court, where the next chapter of the dieselgate story is being written—one that could have consequences for years, if not decades, to come.