News summary produced by Claude AI
A high court judgment rejected the majority of allegations in a major class action lawsuit filed on behalf of 1.6 million UK car owners regarding emissions-cheating technology in diesel vehicles. The case, heard over 15 weeks between October 2025 and March 2026, represented the largest group action trial in English legal history and examined vehicles sold by five manufacturers: Mercedes, Ford, Renault, Nissan, and Peugeot/Citroën.
Lady Justice Cockerill determined that in most instances, the technologies and strategies examined did not meet the legal definition of prohibited defeat devices—software designed to make engines perform differently during emissions testing. However, the judge found that certain technology and strategies employed in some Mercedes and Peugeot-Citroën vehicles could constitute such devices. The claimants had argued that manufacturers deliberately engineered vehicles to reduce nitrogen oxide emissions during test conditions while performing differently under normal driving circumstances. All named manufacturers had denied using prohibited defeat devices.
The judge emphasized that not every emissions-control calibration or strategy qualifies as a defeat device and that proving manufacturer intent to manipulate tests was necessary to establish violations. She noted that establishing the effect of particular technical modifications on emissions reduction was complex and that no testing approach was entirely satisfactory. The ruling indicated that adopting alternative interpretations of defeat device definitions could result in additional violations being identified across the named manufacturers’ vehicles.
The case’s outcome prompted mixed reactions from stakeholders. Car manufacturers, including Mercedes-Benz and Stellantis, welcomed the verdict while noting they were considering appeals regarding specific findings against them. The law firms representing claimants—led by Leigh Day and Pogust Goodhead—said they were exploring appeals, arguing the judgment diverged significantly from established European legal standards on emissions violations. Environmental advocates characterized the ruling as a setback but reiterated concerns about diesel vehicle emissions regardless of legal determinations.