High court rejects most of 'dieselgate' claims brought by 1.6m UK car owners

A UK high court has rejected most of the “dieselgate” claims brought on behalf of 1.6 million owners of polluting cars, a ruling that automakers largely welcomed. Lady Justice Cockerill found that in most cases the court determined that the relevant strategy did not amount to a prohibited defeat device, meaning software that can change engine behavior during emissions tests. However, she said some technologies and strategies used in certain Mercedes and Mercedes and Peugeot-Citroën vehicles could constitute defeat devices. Claimants’ lawyers said they are considering an appeal, warning that the decision creates a significant difference between Great Britain and much of Europe. The trial, the largest group action in English legal history, ran for 15 weeks from October 2025 to March 2026 and focused on 20 vehicles sold by five manufacturers: Mercedes, Ford, Renault, Nissan, and Peugeot/Citroën, though the judgment binds other manufacturers. The judge stressed that proving intent to rig tests was necessary and that reduced effectiveness outside test conditions was not enough. Mercedes-Benz and Stellantis said they are reviewing appeals; Nissan and Renault said their technologies complied with regulations.