On 10 July 2026, Lady Justice Cockerill handed down the liability judgment in the Pan-NOx Prohibited Defeat Device trial, the largest and most complex group claim in English and Welsh legal history, finding that three vehicles, one Mercedes and two Peugeot/Citroën models, contained prohibited defeat devices, while Ford, Renault, and Nissan were found not to have breached emissions regulations. The carmakers broadly claimed victory. But a 2010 internal document from PSA Peugeot Citroën, disclosed during proceedings, offers a more unsettling reading of the industry’s relationship with clean air standards than any court verdict can capture on its own.
The document, written by PSA engineers, notes that one of the company’s emissions-filtering technologies gave it “a competitive advantage” over its rivals and kept it ahead of regulatory requirements. So far, this reads as normal competitive behaviour. The engineers then warn, however, that getting too far ahead would pose a “major” risk. The reason: proving that cleaner emissions were technically achievable beyond what EU law required could give the European Commission “the opportunity to tighten” standards further. The internal logic is explicit. The barrier to regulatory ambition was not technical feasibility. The industry desired to keep regulators from learning what was feasible.
What the Ruling Actually Decided and What It Left Unresolved
The judgment issued by Lady Justice Cockerill after 55 hearing days spanning October 2025 to March 2026 is a partial, technically constrained ruling rather than a definitive assessment of the industry’s conduct. The court rejected many allegations brought by the 1.6 million claimants, finding that not every calibration or emissions-control strategy amounted to a defeat device, and specifying that for a defeat device to be found, there must be an intentional or impermissible purpose of causing the emission control system to operate differently when it senses it is being tested.
That intentionality standard creates a high evidentiary bar that benefits manufacturers. The judgment also departed from key EU case law on how a defeat device is defined, creating a divergence between the legal position in England and Wales and much of Europe. In EU member states, the standard for establishing a prohibited defeat device has been interpreted more broadly. Martyn Day of Leigh Day, representing the claimants, noted that if this ruling is followed in Great Britain, it would be the only significant place in Europe where manufacturers are free to build and sell cars containing these types of devices.
For Peugeot-Citroën-DS, a “split mode” device was found to be a prohibited defeat device; for Renault and Nissan, devices including torque cut-off systems and correction factors were found to breach regulations in earlier proceedings. A further trial is scheduled for October 2026 to consider the consequences of actionable breaches, including questions relating to compensation and other remedies. The damages phase, not the liability finding, will determine the financial exposure that manufacturers face, and with 1.6 million claimants, the potential sums remain substantial.
The Document the Industry Would Have Preferred to Keep Internal
The 2010 PSA note does not describe illegal conduct. It describes strategic conduct: the deliberate management of technological demonstration to avoid tightening the regulatory ceiling. The engineers were not proposing to falsify test results. They were proposing to manage the pace at which the regulator learned what was possible. The distinction matters legally, but not morally or in terms of public health consequences.
This type of regulatory gaming is not unique to automotive emissions. Industries facing environmental or safety regulation routinely manage the disclosure of capabilities, the framing of feasibility studies, and the pace of voluntary improvement to avoid triggering more demanding compliance requirements. What makes the PSA document notable is its candour: it was written explicitly, retained on file, and is now a court exhibit.
The argument that tougher environmental requirements are technically unrealistic has been central to automotive industry lobbying for decades. It was central to the opposition to the Euro 6 standard, to the Dieselgate cleanup, and to more recent debates about CO2 fleet targets and the 2035 combustion engine phase-out date. The PSA note, written 15 years before it became a court document, reveals that at least some of the engineers who made the technology understood the lobby arguments against ambitious standards to be at least partially insincere.
The Regulatory Enforcement Gap That Predates and Outlasts the Verdict
The UK litigation is not the only front on which the legacy of Dieselgate remains unresolved. German authorities concluded in 2023 that Nissan diesel cars contained illegal emissions software, a finding that exposed the persistent failure of EU member states to share information about suspected defeat device cases with each other or with the Commission.
This information gap was identified as a core structural failure after the original 2015 Volkswagen scandal, and the Commission responded with new rules requiring member states to report on their enforcement activities. Member states were legally required to submit compliance reports to the Commission by 1 September 2025. None did. Since then, only four of the EU’s 27 member states have responded. The Commission’s own review, which was due by 1 September 2026, has been pushed back to the end of 2026 or early 2027 as a result.
The pattern is consistent. Ten years after the Volkswagen scandal, the enforcement coordination framework that was supposed to prevent the next Dieselgate from going undetected across borders is operating with 23 of 27 member states either silent or late. The 2010 PSA engineers’ confidence that regulatory tightening could be forestalled by managing technological disclosure may have reflected not only an assessment of the Commission’s political appetite for ambition, but also an accurate reading of national enforcement capacity. The two problems, corporate management of what regulators know, and regulators’ failure to share what they learn, have reinforced each other throughout the post-Dieselgate decade.
