On 10 July 2026, the English High Court reached its decision in the Pan-NOx emissions group litigation [2026] EWHC 1753 (KB). It focused on test cases against five lead vehicle manufacturers: Mercedes-Benz, Ford, Stellantis (owners of Peugeot and Citroën), Renault and Nissan. 

A decisive win for the defendants on the central legal question of what constitutes a "prohibited defeat device" ("PDD") resulted in almost all allegations being dismissed. Mercedes-Benz and Stellantis are considering possible appeals on the small number of allegations which were upheld. The claimants, however, secured a significant consolation in establishing that individual vehicle purchasers have a private law right of action in damages under the applicable legislation. The claimants are also considering an appeal.

Background

The case, which involved approximately 1.6 million claimants, concerns allegations that diesel vehicles manufactured between 2012 and 2017 were fitted with PDDs. The claimants comprised owners of such vehicles, alleging that the PDDs reduce the effectiveness of a vehicle's emissions control system in real-world driving, while performing better in official laboratory tests used for regulatory approval. The defendant manufacturers denied liability, arguing that their emissions strategies complied with the applicable regulatory framework in the EU at the relevant time (specifically the Euro 5 and Euro 6 standards).

The 369-page judgment followed a 10-week trial in October to December 2025, and three weeks of submissions in March 2026. The judgment on the legal issues considered in the test cases binds all parties across the group litigation.

What is a "Defeat Device" (and when is it prohibited)?

The central question regarded statutory interpretation: what, precisely, is a "defeat device" under the applicable EU emissions regulation?

This disputed issue turned on whether the definition was limited to (as the defendants argued) devices that detected when an official emissions test was being conducted (and therefore performed better during that test than in real-world driving), or whether (as the claimants argued) it extended more broadly to any calibration strategy that resulted in higher emissions outside such tests.

Cockerill LJ accepted the defendant manufacturers' narrower interpretation, holding that:

"A defeat device is a device which senses one or more parameters of the test (including its boundary) and objectively operates with the purpose of causing the ECS [emissions control system] to work more effectively when it senses that it is being subjected to a test cycle compared to how it works in out-of-test driving."

The Court concluded that there is a presumption that a defeat device is a PDD, unless a narrow set of exceptions apply under the applicable regulation, such as where the defeat device is justified for the protection of the engine against damage or accident, and for the safe operation of the vehicle.

Decision

Applying this definition, Cockerill LJ rejected most of the claimants' allegations. The principal findings were:

• Ford, Renault and Nissan: all PDD allegations were dismissed in their entirety.

• Mercedes-Benz: all but one PDD allegation was dismissed. The one device found to be prohibited (a coolant temperature manipulation device in one sample vehicle) had already been removed from affected vehicles by a free software update in December 2015.

• Stellantis: all but one PDD allegation was dismissed. A particular fuel injection strategy in certain older sample vehicles was found to be a PDD.

The Court also considered the counterfactual position had it adopted a broader definition of "defeat device." On that alternative analysis, although a greater number of defeat devices would have been found, most allegations would have nevertheless failed, either because the alleged defeat device operated only outside of "normal driving conditions" (for example, by reference to temperature, altitude, and torque/engine speed), or because no actual reduction in the effectiveness of the emissions control system had been established.

Impact of the decision

Three aspects of the judgment are likely to have significance beyond the diesel emissions litigation. The judgment on the one hand may make England & Wales a more attractive jurisdiction to bring private law claims in relation to breaches of regulatory standards, particularly where EU case law is deemed less favourable to claimants. On the other hand, the unfavourable result for the litigation-funded claimants may raise the perceived risk profile of large-scale group litigation in England & Wales.

(1) Availability of private law claims

First, the Court opened the door to further claims based around the argument that technical, regulatory standards can found a private cause of action, even where the no specific provision says so in terms. In its judgment, the Court confirmed that individual vehicle owners can sue manufacturers directly for damages where a PDD is found in their vehicle, even though the EU emissions regime is, on its face, a piece of public regulation, rather than consumer protection regulation. The defendants had argued (unsuccessfully) that the statutory regime is a public/regulatory enforcement framework and does not give rise to private law claims. In finding for the claimants on this point, Cockerill LJ clarified that where an EU regulation forms part of a broader legislative scheme which, read as a whole, is intended to protect individuals and requires the right to bring a private damages claim, that protective purpose satisfies the established English law test for whether such a claim is available.

The Court did however reject the claimants' separate argument that the mere presence of a PDD automatically constitutes a breach of a buyer's purchase contract, as implied terms under English law as to the satisfactory quality of the cars in question require the Court to take into account all the circumstances surrounding the inclusion of a PDD. The Court therefore concluded that "Arguments relating to breach of contract would require fuller evidence before a conclusion could be reached". Therefore while the door to claims for breach of contract is open, claimants cannot skip the more detailed evidential work required to prove their case.

(2) Applicability of Post-Brexit EU Case Law

Secondly, the judgment addresses how English Courts should treat decisions of the Court of Justice of the European Union ("CJEU") handed down after the UK's departure from the EU, confirming that the English Court's discretion on this question is "not confined or defined by a requirement for compelling or weighty reasons". In short:

• Pre-Brexit CJEU authority remains binding on the issues it properly determines;

• Post-Brexit CJEU authority which "follows or is logically predicated on" binding pre-Brexit authority will "almost always" be followed; and

• Absent such an underpinning of pre-Brexit authority, post-Brexit authority is not binding, "but is something which may be taken into account, if in all the circumstances of the case the court considers it appropriate to do so."

Applying this framework, Cockerill LJ declined to follow the post-Brexit CJEU ruling in Case (C-128/20) GSMB Invest GmbH & Co v Auto Krainer ("GSMB Invest") which has been highly influential across European Courts and regulators. She concluded that GSMB Invest was premised on a factual error originating from the referring Court, and contained material flaws in its legal reasoning.

This important clarification of the status of post-Brexit CJEU authorities in England & Wales is likely to result in a meaningful divergence between the legal position in this jurisdiction and that prevailing in the EU.

(3) Litigation funding

Third, in the context of ongoing uncertainty as to the timetable for proposed government reforms (see our blog here) to the litigation funding industry in England & Wales, the judgment may have a stalling effect on the funding of large-scale group litigation in the short term. Renault Group has published a press release confirming that it "will now pursue the recovery of its legal costs from the large institutional insurers and hedge funds who backed these claims in the hope of financial gain".

What's next?

A further trial is currently listed for October 2026 to "resolve quantum issues in relation to the claims for breach of contract and statutory duty only". This will establish how claimants will be able to calculate possible compensation for the breach of statutory duty claims already established by the judgment, and the breach of contract claims, should liability be established for such claims at a later date.

In addition, Cockerill LJ observed that "it is close to a certainty that determined attempts will be made to appeal this decision". Both the claimants and certain defendant manufacturers have indicated they are considering potential appeals. It may be that this is not the final destination for "Dieselgate"…