Dieselgate trial set to begin

The long-awaited trial regarding the Dieselgate emissions cheating scandal is set to commence in the High Court on Monday 13 October 2025 at 10.30am. This case marks a significant milestone as it is the largest group claim trial in English and Welsh legal history, with 1.8 million vehicle owners challenging 14 major car manufacturers over allegations that they manipulated emissions tests.

The case centres around accusations that diesel vehicles, including those from Mercedes, Ford, Renault, Nissan, and Peugeot/Citroen, were sold with technology designed to deceive legal emissions standards from 2009 onwards. Vehicle owners contend that these cars were equipped with “cheat devices” or “prohibited defeat devices (PDDs)” within their engine management systems. Under test conditions, these devices allegedly allowed vehicles to emit harmful pollutants like nitrogen oxides and particulates at legal levels, but when driven normally, they emitted significantly higher levels, thereby contributing to environmental damage and posing health risks to the public.

The High Court has designated the five lead defendants in this group claim trial, which will last approximately three months. Notably, other manufacturers faced with similar allegations include Vauxhall/Opel, Volkswagen/Porsche, Jaguar Land Rover, BMW, FCA/Suzuki, Volvo, Hyundai-Kia, Toyota, and Mazda. Their cases will be determined by the outcome of the lead trial, a process necessitated by the sheer scale of the claims.

Lawyers from Leigh Day, in collaboration with 21 other law firms, represent the affected vehicle owners. Leigh Day’s senior partner Martyn Day expressed the significance of the trial, stating, “A decade after the Dieselgate scandal first came to light, 1.6 million UK motorists now get their chance to establish at trial whether their vehicles contained technology designed to cheat emissions tests.” He continued, highlighting the potential implications of the case, “Fourteen of the biggest car manufacturers operating in the UK are facing these claims which, if proven, would demonstrate one of the most egregious breaches of corporate trust in modern times.”

Among the vehicle owners participating in the trial is Mercedes driver Adam Kamenetzky from London, who stated, “If these allegations are true, the regulators, the politicians and the public have been cheated by manufacturers who, it’s claimed, are profiting from their sale of diesel cars while flouting clean air laws and measures such as ULEZ.” He further emphasised the broader public health implications of the issue, saying, “This is not just a personal issue, but one of much wider public concern: air pollution is a leading cause of ill health and premature death around the world.”

As the trial approaches, public awareness of the ongoing impact of the Dieselgate scandal is heightened, with stakeholders including environmental groups like Mums for Lungs and ClientEarth expected to vocalise their concerns outside the Royal Courts of Justice prior to the hearing. The High Court's judgment, anticipated in summer 2026, aims to provide clarity on the legal landscape surrounding these emissions claims and mitigate the need for further trials regarding PDDs in diesel vehicles. A subsequent trial to determine financial compensation is scheduled for autumn 2026.