Key Takeaways
- The UK High Court largely rejected the “dieselgate” claim against major car manufacturers, finding that most emissions‑control strategies did not amount to prohibited defeat devices.
- However, certain calibrations used in some Mercedes‑Benz and Peugeot‑Citroën models were deemed to constitute defeat devices, leaving those manufacturers exposed to potential liability.
- Lady Justice Cockerill emphasized that proving intent to cheat tests is required; merely showing reduced effectiveness of emissions controls outside test conditions is insufficient.
- The judgment creates a legal divergence between the UK and much of Europe, where broader interpretations of “defeat device” have led to more findings of illegality.
- Manufacturers welcomed the ruling but indicated they may appeal specific adverse findings; claimants are also considering an appeal to align UK law with EU precedent.
- The decision does not alter the scientific consensus that the diesel vehicles in question emit harmful levels of nitrogen oxide (NOx) in real‑world driving.
Background of the Litigation
The case represents the largest group‑action trial in English legal history, brought on behalf of approximately 1.6 million UK owners of diesel cars alleged to contain illicit defeat‑device software. More than 20 law firms, led by Leigh Day and Pogust Goodhead, pursued the claim against five manufacturers—Mercedes‑Benz, Ford, Renault, Nissan, and Peugeot/Citroën—covering 20 vehicle models sold from 2009 onward. The litigation followed the revelations a decade earlier that Volkswagen had programmed its engines to emit lower NOx levels during laboratory tests than during ordinary road use, a practice that sparked worldwide regulatory scrutiny and numerous similar lawsuits across Europe and the United States.
Legal Standard Applied by the Court
Lady Justice Cockerill’s judgment clarified the legal test for what constitutes a prohibited defeat device under UK law. She held that simply demonstrating that a calibration reduces the effectiveness of an emissions‑control system outside test conditions is not enough; the claimants must also prove that the manufacturer intended to rig the test results. The judge stressed that “not every calibration or emissions‑control strategy amounts to a defeat device,” thereby setting a higher evidentiary bar than that applied in many EU jurisdictions, where the mere effect on real‑world NOx emissions can suffice to trigger liability.
Findings Regarding the Manufacturers
In the majority of instances, the court concluded that the strategies employed by the manufacturers did not meet the stringent definition of a defeat device. Consequently, the claims against Ford, Renault, and Nissan were largely dismissed. However, the judge identified specific technologies in certain Mercedes‑Benz and Peugeot‑Citroën vehicles that could constitute defeat devices, noting that the functionality had been removed from those models in 2015. Mercedes‑Benz acknowledged the ruling as “very largely in favour” but indicated it is reviewing the possibility of an appeal concerning the adverse finding. Stellantis, owner of Peugeot‑Citroën, similarly said it is contemplating an appeal over the upheld allegations.
Manufacturers’ Responses and Statements
Nissan reiterated that its vehicle technologies had never been intended to function as defeat devices and maintained compliance with all regulatory requirements. Renault echoed this sentiment, asserting that its cars were “designed, engineered, and manufactured in accordance with all applicable regulatory requirements.” Ford, which was contacted for comment, has not issued a public statement at the time of reporting. The overall tone from the manufacturers was one of relief, with many welcoming the judgment as vindication of their engineering practices, while simultaneously reserving the right to challenge the limited adverse findings.
Claimants’ Reaction and Prospects for Appeal
Leigh Day described the ruling as “disappointing,” arguing that it permits defeat devices in the UK that would likely be deemed illegal across the European Union. Senior partner Martyn Day contended that the High Court had found that other manufacturers, besides Volkswagen, had employed VW‑style defeat devices, yet the judge’s narrow interpretation of the law rendered many of those devices lawful. Pogust Goodhead’s Anna Varga warned that the judgment does not conclude the litigation; while certain manufacturers were found to have installed unlawful defeat devices, the court adopted a significantly narrower definition of “defeat device” than that applied elsewhere in Europe. Both firms indicated they are considering seeking permission to appeal the decision in order to align UK jurisprudence with the broader EU approach.
Public Health and Environmental Perspective
The campaign group Mums for Lungs characterized the outcome as a setback but stressed that the court’s findings do not alter the scientific consensus: the diesel vehicles in question remain toxic contributors to NOx pollution, which is linked to respiratory illnesses and environmental degradation. Director Jemima Hartshorn urged the two manufacturers identified as having unlawful defeat devices to act swiftly—removing the offending vehicles from circulation and providing appropriate compensation to affected owners. This stance underscores the ongoing tension between legal determinations of liability and the broader public‑health imperative to reduce urban air pollution.
Implications for Future Regulation and Litigation
The judgment highlights a growing legal divergence between the UK and the EU regarding the interpretation of defeat‑device provisions. Should the UK maintain its narrower stance, manufacturers may face less stringent legal exposure domestically compared with their European counterparts, potentially influencing decisions about where to allocate resources for emissions‑control technology upgrades. Conversely, if claimants succeed in an appeal that adopts a more expansive EU‑style definition, the UK could see a wave of additional litigation akin to the continental dieselgate cases. The case also serves as a reminder that robust, real‑world emissions testing and transparent regulatory standards are essential to prevent future discrepancies between laboratory performance and actual road‑world impacts.
Conclusion
The High Court’s decision delivers a mixed verdict for the parties involved: a substantial vindication for most manufacturers, yet a clear warning for Mercedes‑Benz and Peugeot‑Citroën regarding specific calibrations that may constitute unlawful defeat devices. While the legal battle may continue through appeals, the ruling reinforces the necessity of aligning legal definitions with scientific evidence on vehicle emissions, ensuring that both corporate accountability and public‑health objectives are adequately addressed.