HIGH COURT REJECTS MOST CLAIMS IN UK 'DIESELGATE' GROUP ACTION

The High Court has rejected the majority of allegations in a group action brought on behalf of 1.6 million UK car owners who claimed manufacturers had fitted devices to manipulate emission test results. Lady Justice Cockerill ruled that in most cases, the technology and strategies used did not constitute prohibited defeat devices — software that allows engines to perform differently during tests than in normal driving. The judge found that strategies employed in some Mercedes and Peugeot-Citroën vehicles could constitute defeat devices, but rejected claims against the other three manufacturers in the case: Ford, Renault and Nissan.

The claim, heard over 15 weeks between October 2025 and March 2026, was the largest group action trial in English legal history and examined 20 vehicles sold by five manufacturers from 2009 onwards. Claimants had argued that manufacturers engineered vehicles to reduce nitrogen oxide emissions in tests whilst performing worse in normal driving conditions. The manufacturers denied using prohibited defeat devices. Lady Justice Cockerill stated that manufacturers must have intended to rig tests for a strategy to constitute a defeat device, and that merely reducing emissions-control system effectiveness outside testing conditions was insufficient evidence.

Lawyers representing the claimants stated they were considering an appeal, citing a significant divergence between the legal position in Great Britain and that in much of Europe. Mercedes-Benz said the court had ruled "very largely in favour" of the manufacturer but indicated it was considering appealing the finding regarding one vehicle deemed non-compliant. The judgment's interpretation of defeat devices will apply to other manufacturers beyond those directly involved in the case.