A major legal battle over diesel vehicle emissions in England and Wales is continuing after London’s High Court refused permission on 8 October 2026 for motorists to appeal a ruling that largely favoured several major car manufacturers. The case involves around 1.6 million claimants who allege that diesel vehicles contained unlawful emissions-control systems designed to manipulate pollution tests.
The decision is a setback for the motorists, but it does not end the litigation. Lawyers representing the claimants have said they intend to apply directly to the Court of Appeal, seeking another opportunity to challenge the July judgment.
The lawsuit followed the Volkswagen Dieselgate scandal, which came to international attention in 2015 after the company admitted that software in millions of diesel vehicles had been used to manipulate emissions tests. The scandal triggered investigations, regulatory action and lawsuits across several countries, while raising wider questions about whether vehicle emissions controls performed as expected during normal driving.
The current UK case concerns vehicles manufactured by Mercedes-Benz, Ford, Nissan, Renault and Stellantis-owned brands Peugeot and Citroën. The claimants argue that certain systems fitted to the vehicles amounted to prohibited “defeat devices”, meaning they could alter emissions-control performance in ways that breached applicable regulations.
The trial began in October 2025 and examined 20 sample vehicles intended to help the court assess issues relevant to the wider group litigation. In its ruling on 10 July 2026, the High Court rejected most of the allegations concerning those vehicles. The court found that only three of the 20 sample vehicles contained devices that met its legal definition of prohibited defeat devices: one Mercedes vehicle and two Peugeot or Citroën models.
The other 17 sample vehicles were found not to contain devices that met the court’s definition, although the claimants’ lawyers dispute the legal approach taken in reaching those conclusions. The July decision was therefore broadly favourable to the manufacturers, while leaving some allegations upheld.
The latest ruling concerns whether the claimants could appeal through the judge who presided over the trial. Judge Sara Cockerill refused that request during a hearing on 7 and 8 October. She said she would provide her full reasons in writing at a later date.
Martyn Day, senior partner at Leigh Day, one of the law firms representing the motorists, said the claimants were disappointed but would continue pursuing the case.
While we are obviously disappointed with the decision, this is far from the end of the road for the 1.6 million clients bringing a legal claim over Dieselgate.
Day said the legal team considered the July judgment to have adopted an overly narrow definition of a prohibited defeat device. The claimants also argue that the court’s interpretation diverges from decisions made elsewhere in Europe and that some of the technical evidence requires further examination.
We believe the judgment contradicts EU law and intend to seek permission to appeal directly at the Court of Appeal to ensure that these issues are thoroughly re-examined.
The proposed appeal is significant because the dispute is not simply about whether a particular vehicle passed a laboratory emissions test. It also concerns how the law defines unlawful emissions-control technology, including the circumstances in which a vehicle’s system may behave differently during testing and normal use.
Diesel vehicles rely on emissions-control systems to limit pollutants such as nitrogen oxides, commonly known as NOx. These pollutants contribute to air pollution and can harm human health. The legal dispute centres on whether particular systems were designed or operated in a way that falls within the regulatory definition of a prohibited defeat device.
The court’s interpretation of that definition has implications beyond the sample vehicles. If the July judgment stands, it could restrict the circumstances in which claimants can establish that emissions-control technology breached the relevant rules. If an appeal succeeds and the legal interpretation changes, the findings concerning the sample vehicles and the wider claims could require further consideration.
The claimants’ lawyers have also argued that the judgment creates a difference between the position in England and Wales and the approach taken across much of the European Union. Their argument is that certain devices which may be considered unlawful under European Union law could be treated differently under the interpretation adopted by the UK court.
That disagreement is part of the broader legal background following the United Kingdom’s departure from the European Union. Although the UK has retained much of its existing vehicle emissions framework, the interpretation and application of retained rules can become contested when courts consider earlier European judgments.
The manufacturers have largely succeeded at the liability stage of this case, but the dispute is not yet resolved. The next important development will be whether the Court of Appeal grants permission for the claimants to challenge the judgment and, if it does, which parts of the legal reasoning will be examined.
The scale of the litigation adds another layer of complexity. With approximately 1.6 million motorists involved, the case requires the courts to assess technical evidence from a limited group of sample vehicles while determining how those findings apply across a much larger number of claims. Any change in the legal interpretation could affect the next stages of the proceedings.
The case also demonstrates the difficulty of resolving mass claims involving complex engineering. Establishing whether a vehicle contains a prohibited defeat device requires more than identifying high emissions in isolation. The court must assess how the emissions-control system operates, the circumstances in which it changes behaviour and whether that behaviour falls within the legal definition of prohibited technology.
For motorists, the litigation concerns potential legal remedies relating to vehicles they bought or used. For manufacturers, it involves questions about compliance, liability and the legal standards applied to emissions-control systems. For regulators and policymakers, the dispute illustrates how the effectiveness of emissions rules depends partly on how courts interpret and enforce them.
The legal proceedings also remain distinct from the wider environmental consequences of diesel pollution. The court’s findings on whether particular devices meet a legal definition do not, by themselves, establish the overall air-quality impact of every vehicle involved. Equally, the presence of elevated emissions does not automatically prove that a manufacturer used an unlawful defeat device. Those questions require evidence and must be assessed separately.
The manufacturers have not been found liable for most of the alleged defeat devices in the 20 sample vehicles examined at trial, while three vehicles were found to contain devices meeting the court’s definition. The claimants are now seeking permission to challenge the legal reasoning behind the broader ruling.
The next stage will depend on the Court of Appeal’s response to the proposed application. Until that process advances, the July judgment remains the central ruling in the case, and the motorists’ wider claims remain subject to the ongoing litigation.