A decade after the ‘dieselgate’ scandal emerged, a lawsuit against five leading carmakers potentially worth up to £6bn has opened in London’s High Court.
The Pan-NOx group litigation, before The Honourable Lady Justice Cockerill DBE, involves some 1.6 million claimants and is scheduled to run for three months, with a hearing to determine the amount of any compensation set for October 2026.
The court will hear allegations that these companies deliberately misled motorists by using unlawful software known as ‘prohibited defeat devices’ (PDDs) to cheat emissions tests.
The claimants allege these devices lowered emissions during official testing, but once the vehicles were on the road, they emitted pollution levels above the legal limit.
Twenty sample diesel vehicles, produced from 2012 to 2017 by the five manufacturers, will be assessed as to whether they contained prohibited defeat devices and, if so, whether the presence of the devices gives rise to claims for breach of contract and breach of statutory duty.
The defendants – Mercedes, Ford, Peugeot/Citroën, Renault and Nissan – deny liability. Volkswagen previously settled a related group action in 2022 in which Harcus Parker acted for the claimants.
The five companies were selected as lead defendants to be tried first, followed by nine other manufacturers accused by 220,000 car owners of misleading them over emissions tests.
Alicia Alinia, CEO at Pogust Goodhead, one of the lawyers for claimants, said: “The case goes to the heart of corporate accountability and environmental justice. The court will test whether prohibited defeat devices were used to game emissions rules and, if so, what impact they have had on the air we all breathe, and the health of people exposed to higher levels of harmful pollution.”
Alinia added: “The judgment will guide the remaining UK claims and, we hope, send a clear signal to the broader industry on compliance and consumer trust.”
Pogust Goodhead had made a voluntary application to stand down as lead solicitor in the litigation shortly before the start of the trial, in a highly unusual move that followed the departure in August of the firm’s co-founder and former chief executive, Tom Goodhead, and the subsequent exit of at least five lawyers involved in the dieselgate litigation, the Financial Times reported.
The application was refused, however. Pogust Goodhead commented: “We welcome Lady Justice Cockerill’s decision that the status quo is the best course at this time, which means that Pogust Goodhead will continue as lead solicitor, along with Leigh Day. We are fully committed to successfully litigating this historic case and remain focused on the pursuit of justice for the millions of people affected by the UK diesel emissions scandal.”
The lead claimants were previously chosen as Pogust Goodhead, Leigh Day, Slater & Gordon, Hausfeld, Milberg and KP Law in various combinations. For eight GLOs, the joint lead solicitors are Pogust Goodhead and Leigh Day. For four others, it is Pogust Goodhead alone. For one, it is Milberg and KP Law.
Tom de la Mare KC, of Blackstone Chambers, opened for the claimants, saying in his skeleton arguments that “each player in the industry basically took a conscious decision that customer convenience, which helped the industry sell more cars, was more important” than cutting emissions.
There are 22 separately represented defendant groups, represented by Freshfields, Kennedys and Cleary Gottlieb, among others, and associated counsel teams, with more than 20 leading counsel instructed.
A spokesperson for Mercedes said the mechanisms used in tests were “justifiable from a technical and legal standpoint”. Other manufacturers issued similar statements in their skeleton arguments, arguing the claim was “without merit and untenable”.
The trial follows earlier costs hearings in the group litigation, preceded by a two-day hearing in July 2025 during which claimants sought litigation budgets totalling £47m. In court, the budgets were reduced by £25m, giving the claimants a combined budget of £22m. That followed a 2024 ruling that criticised the “staggering” costs of the litigation. The court reduced the original £650m legal costs bill, significantly cutting the claimants’ budgeted costs by nearly 75%, and described the claimant budgets as “absurd” and “eye-watering”.
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