Not every calibration amounts to a defeat device
In the summer of 2026, a British high court concluded the largest group action trial in English legal history by largely absolving five major carmakers of deliberately deceiving emissions regulators — a verdict that turned less on what the cars actually emitted and more on what the law required claimants to prove. Lady Justice Cockerill drew a demanding line between vehicles that performed differently on the road than in test conditions and vehicles that were intentionally engineered to deceive, finding that most manufacturers had not crossed it. The ruling leaves 1.6 million UK car owners with limited legal recourse, while exposing a meaningful rift between how British courts and their European counterparts understand the very meaning of a defeat device.
- Over 1.6 million UK drivers had staked their claims on a decade-old scandal's logic — that carmakers, like Volkswagen before them, had secretly tuned diesel engines to pass tests they were never designed to pass in real life.
- The court's central tension was not scientific but definitional: Lady Justice Cockerill required proof of intentional test-rigging, a threshold the claimants' evidence — clouded by genuinely murky emissions science — could not reliably clear.
- Only Mercedes and Peugeot-Citroën vehicles were found potentially non-compliant, while Ford, Renault, and Nissan walked away largely vindicated, fracturing what claimants had hoped would be a sweeping industry reckoning.
- The judge herself acknowledged that under EU legal standards, the outcome would likely have been far broader — a candid admission that British law, as she interpreted it, sits in a different universe from the standards prevailing across Europe.
- Claimants' lawyers at Leigh Day and Pogust Goodhead are weighing an appeal, arguing the ruling adopted a dangerously narrow reading of defeat device law and that the litigation is far from over.
On a July morning in 2026, Lady Justice Cockerill delivered her verdict in the largest group action trial in English legal history — and largely sided with the carmakers. After fifteen weeks of testimony spanning late 2025 into early 2026, she ruled that most of the allegations brought by 1.6 million UK diesel car owners against Ford, Renault, Nissan, Mercedes, and Peugeot-Citroën did not meet the legal standard required to establish the use of prohibited defeat devices.
The claimants had argued that these manufacturers followed the Volkswagen playbook — fitting vehicles with software that suppressed nitrogen oxide emissions during regulatory tests while allowing them to surge during ordinary driving. But Cockerill drew a sharp distinction between cars that simply performed differently under test conditions and cars that were deliberately engineered to deceive. Proving the latter, she found, required a level of evidence the claimants could not supply. The emissions science itself, she noted, was difficult enough to interpret that no analytical approach was entirely satisfactory.
The exceptions were Mercedes and Peugeot-Citroën, whose vehicles were found to potentially contain defeat devices. Both companies indicated they were considering appeals. Ford, Renault, and Nissan were largely cleared and welcomed the ruling. Yet the judgment contained a striking admission: Cockerill acknowledged that under EU legal interpretation, a larger number of defeat devices — including in each of the lead manufacturers' cars — would have been established. British law, as she read it, demanded more.
For the claimants' legal teams, that divergence was the heart of the matter. Martyn Day of Leigh Day noted that the judge had actually found other manufacturers used VW-style defeat devices, yet the narrower British definition meant they faced little consequence. Anna Varga of Pogust Goodhead said the ruling did not end the litigation and had adopted an interpretation significantly out of step with European standards.
For the 1.6 million car owners, the practical reality was blunt: they had purchased vehicles that emitted far more nitrogen oxide on real roads than regulators had approved, and they had largely lost their legal case. Jemima Hartshorn of Mums for Lungs called it a setback but held firm on the underlying facts — whatever the courts decided, the science on diesel toxicity had not changed. Whether an appeal can bring British law into closer alignment with Europe now becomes the defining question.
On a July morning in 2026, a British high court delivered a verdict that will reshape what it means to cheat an emissions test—at least in the eyes of English law. Lady Justice Cockerill, after presiding over 15 weeks of testimony between October 2025 and March 2026, ruled that the vast majority of allegations brought by 1.6 million UK car owners against five major manufacturers did not hold water. The case, the largest group action trial in English legal history, had asked a deceptively simple question: Did carmakers deliberately engineer vehicles to behave differently during emissions tests than they did on the road? The manufacturers said no. The court, largely, agreed.
The claimants had argued that companies including Ford, Renault, Nissan, Mercedes, and Peugeot-Citroën had fitted their diesel vehicles with software designed to reduce nitrogen oxide emissions—a toxic pollutant—when the cars were being tested, while allowing those emissions to spike during normal driving. This was the playbook Volkswagen had followed, a scandal that erupted more than a decade earlier and sent shockwaves through the industry. But Cockerill's judgment drew a sharp distinction between what the claimants could prove and what the law actually required. "Not every calibration or emissions-control strategy amounts to a defeat device," she wrote. The court would need evidence of intentional deception—proof that manufacturers had rigged the test itself, not merely that their cars performed differently under test conditions than in the real world.
This interpretation proved decisive. In the majority of cases, Cockerill found, the manufacturers had not crossed that threshold. They had engineered vehicles with various emissions-control strategies, yes, but the court could not establish that these were deliberately designed to fool regulators. The burden of proof, in other words, was steep. The judge acknowledged the difficulty: "Testing, however, is difficult to interpret and none of the approaches to isolating the effect of a particular calibration on NOx was entirely satisfactory." She was saying, in effect, that the science itself was murky enough that the claimants could not definitively prove what they alleged.
There were exceptions. Mercedes and Peugeot-Citroën vehicles were found to potentially contain defeat devices. Mercedes said the functionality in question had been removed from its cars in 2015 and indicated it was considering an appeal. Stellantis, which owns Peugeot-Citroën, said the same. Ford, Renault, and Nissan were largely cleared. All four manufacturers welcomed the ruling. The verdict, however, exposed a chasm between British law and the legal standards applied across much of Europe. Cockerill herself noted in her judgment that "if an alternative approach to the meaning of 'defeat device' were taken a larger number of defeat devices would be established, including devices in each of the lead manufacturers cars." She was acknowledging that under EU interpretation—the standard that had prevailed in other jurisdictions—the outcome might have been entirely different.
The claimants' legal team, led by firms including Leigh Day and Pogust Goodhead, called the ruling disappointing and said they were weighing an appeal. Martyn Day, a senior partner at Leigh Day, pointed out that the judge had actually found that other manufacturers, like Volkswagen, had used defeat devices—yet the narrower definition of what constitutes a defeat device under British law meant those manufacturers walked away largely unscathed. "The high court has found that despite their denials, other manufacturers also used VW-style defeat devices," Day said. "The judge has also found that many other defeat devices are lawful because she surprisingly disagreed with the established EU case law on what a defeat device is." Anna Varga of Pogust Goodhead echoed the sentiment: the judgment, she said, "does not bring this litigation to an end," and it had adopted "a significantly narrower interpretation of the law than that applied elsewhere in Europe."
For the 1.6 million owners of these vehicles, the practical consequence was stark. They had purchased cars that emitted far more nitrogen oxide on the road than manufacturers had disclosed or regulators had approved. They had breathed that pollution. They had sought legal remedy. And now, in the largest group action trial in English history, they had largely lost. Jemima Hartshorn, director of the campaign group Mums for Lungs, called the verdict a setback but insisted it changed nothing about the underlying science. "Whatever the courts have found, it does not change the scientific consensus—that these diesel cars are toxic," she said. The question now is whether the claimants will pursue an appeal, and whether that appeal might force British courts to reckon with the legal standards that have prevailed in Europe—standards that might have produced a very different outcome.
Citações Notáveis
In the majority of instances, the court found that the relevant strategy did not constitute a prohibited defeat device— Lady Justice Cockerill
The high court has found that despite their denials, other manufacturers also used VW-style defeat devices. The judge has also found that many other defeat devices are lawful because she surprisingly disagreed with the established EU case law on what a defeat device is.— Martyn Day, Leigh Day
A Conversa do Hearth Outra perspectiva sobre a história
Why does the British court's definition of a defeat device matter so much when the EU has already settled on a different one?
Because 1.6 million people live in Britain, not the EU. A defeat device under EU law might be perfectly legal under British law. The judge even said so—she acknowledged that if she'd used the EU definition, many more manufacturers would have been found guilty. But she didn't. So the law diverges, and the people seeking compensation are stuck on the wrong side of that line.
But the judge found that Mercedes and Peugeot-Citroën did use defeat devices. So it's not a total loss for the claimants, is it?
It's a partial loss. Two manufacturers out of five. And even those two are considering appeals. The claimants wanted to establish a pattern—that the whole industry had done this, the way Volkswagen had. Instead, they got a ruling that says most of the industry didn't, or at least didn't in a way the court could prove under British law.
What's the practical difference between a car that reduces emissions during tests and one with a "defeat device"?
Legally, everything. Practically, nothing. The car still emits more pollution on the road than in tests. The people breathing that air don't care what the software is called. But the court needed proof of intentional deception—that the manufacturers deliberately rigged the test. Just showing the cars performed differently wasn't enough.
So the claimants' lawyers are appealing?
They're considering it. They'd have to argue that the judge got the law wrong, that British courts should align with the EU standard. It's a long shot, but the alternative is accepting that defeat devices are legal in Britain when they're not in Europe.
What happens to the car owners in the meantime?
They keep driving the cars, or they don't. Either way, they don't get compensated. The ruling stands unless an appeal overturns it. And that could take years.