Cockerill LJ has today delivered judgment following the ‘PDD Trial’ in the Pan-NOx Group Litigation: Various Claimants v Mercedes Benz Group and others [2026] EWHC 1753 (KB). These large-scale proceedings involve claims on behalf of millions of diesel vehicle owners against most of the major car manufacturers, alleging historic breaches of EU emissions regulations.
The PDD Trial was an important and ground-breaking test case of the Claimants’ allegations that almost every diesel vehicle produced under the Euro 5 and Euro 6(b) emissions standards (applicable to new vehicles from approximately 2009 to 2016) contained prohibited ‘defeat devices’ (PDDs) in breach of Articles 3(10) and 5(2) of Regulation (EC) 715/2007 (the Emissions Regulation).
A selection of Sample Vehicles, in various software iterations, was selected from five Lead Defendant manufacturers: Mercedes-Benz, Ford, Peugeot/Citroën, Renault and Nissan. As well as determining the defeat device allegations against those manufacturers, the trial was intended to provide broadly applicable guidance across the rest of the Pan-NOx cohort, which also encompasses claims against BMW, FCA/Suzuki, Hyundai/Kia, JLR, Mazda, Porsche, Toyota, Vauxhall, Volvo and VW. Following a vehicle testing programme and extensive documentary disclosure, factual and expert evidence was heard over 10 weeks in October-December 2025, followed by three weeks of submissions and legal argument in March 2026.
The Claimants alleged around 40 different types of ‘defeat device’ in the Sample Vehicles, relating to the design and calibration of three emissions control technologies: Exhaust Gas Recirculation (EGR), Lean NOx Trap (LNT) and Selective Catalytic Reduction (SCR): see Judgment at [9] and [359]-[388].
In a comprehensive 321-page judgment, Cockerill LJ has dismissed all the defeat device allegations made against Ford, Nissan and Renault: see Judgment at [9], [784], [877], [880], [882-3] and the summary table at pages 303-4. This clears these three manufacturers of all the allegations of regulatory breach advanced at the trial, which are an essential element of the Claimants’ claims for damages and other financial compensation.
Cockerill LJ dismissed all but one of the allegations made against each of Mercedes and Peugeot-Citroën, against whom limited findings were made. The Court only found PDDs in relation to a particular EGR device in the original calibration of one of the Mercedes Sample Vehicles (which was removed from affected vehicles some years ago by a software update) and an aspect of the fuel injection calibration in the Euro 5 Peugeot-Citroën Sample Vehicles: [879], [881], [900]-[921] (Mercedes) and [1171]-[1225] (Peugeot-Citroën).
The decisive legal issue concerned the meaning of ‘defeat device’ in Article 3(10) of the Emissions Regulation. Rejecting the various broader interpretations advanced by the Claimants, Cockerill LJ held 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 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”: [661]. In other words, a defeat device is what was referred to at trial as a ‘cycle recognition defeat device’ (CRDD). While recognising that the legislation is not easy to interpret, Cockerill LJ concluded that the CRDD reading fits best with the language, context and purpose of the provisions and, given the practical implications of the different readings, is “the only workable solution”: [599]-[660]; [993].
In the PDD Trial, Cockerill LJ was bound by and followed the decision of the European Court of Justice (CJEU) in CLCV (Case C-693/18), decided a few days before Brexit Implementation Period Completion Day (IPCD) on 31 December 2020 ([242]-[250]); but she declined to follow certain aspects of the non-binding ‘post-Brexit’ CJEU decisions. In particular, Cockerill LJ declined to follow the post-IPCD decision in GSMB Invest (Case C-128/20) which has been influential on recent domestic European case-law and on regulatory approaches to assessing historic regulatory compliance: [264]-[277]. She held it was right not to follow GSMB Invest because the CJEU’s decision was premised on a significant factual misapprehension deriving from the referring court’s reference and had material flaws in its legal reasoning. She also noted that the CJEU was working from a vastly less detailed and developed factual and expert evidence base than was before the English court at the PDD Trial.
The Court determined various other legal issues concerning the interpretation of the exceptions to the defeat device prohibition in Article 5(2) of the Emissions Regulation (see at [662]-[783] and summary at [866]-[874]) as well as two issues relevant to actionability, i.e. the ability of individual claimants to bring civil claims for emissions breaches. At [797]-[850] and [875], the Court concluded that the statutory scheme for emissions regulation requires the creation of a private law right of action by individual claimants. At [851]-[863] and [876], the Court held that the existence of a PDD was not, per se, a breach of the Claimants’ contracts with the car dealership defendants, and any breach of contract would need to be proved on the basis of full evidence, if pursued.
Further court hearings in the coming months will consider the consequences of the PDD Trial Judgment for the claims against the Lead Defendants and for the Pan-NOx litigation as a whole.
Stephen Auld KC, Michael d’Arcy, Simon Gilson and Katherine Boucher acted for the Nissan Defendants, with Anneli Howard KC of Monckton Chambers, instructed by Hogan Lovells Cadwalader (Valerie Kenyon, Neil Mirchandani and team).
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