Hausfeld to seek permission to appeal ‘Dieselgate’ trial judgment for Mercedes claimants
Hausfeld, together with other law firms representing motorists in the Nox litigation, will seek permission to appeal the trial judgment at a High Court hearing from 7-8 October 2026 for its Mercedes claimants.
The judgment, handed down on 10 July following a 13-week trial, found that just three of the 20 representative, including one Mercedes model, were found to have contained so-called Prohibited Defeat Devices (PDDs), which meant they were designed to reduce their emissions output under test conditions compared to when driven on the road.
The other 17 vehicles were found by the judge to contain devices that did not meet the court’s definition of a PDD - and therefore did not breach emissions regulations.
The judgment creates a significant divergence between the legal position in England and Wales compared with much of Europe after the court decided not to follow several key decisions of the Grand Chamber of the Court of Justice of the European Union (CJEU) post-Brexit. This means defeat devices likely to be unlawful in the EU are currently permitted in England and Wales.
The appeal is sought on the following grounds:
- The judge's interpretation of Article 3(10) of the Emissions Regulation led her to adopt an overly narrow definition of a PDD, requiring the presence of a specific type of test-recognition device similar to those in Volkswagen vehicles found to have cheated emissions tests at a previous High Court hearing in 2020.
- The court’s judgment is inconsistent with several CJEU authorities and places the UK in a materially different position from the EU.
- The claimants believe the judge's approach to "normal driving conditions" should be re-examined as it may have been defined too narrowly.
In her judgment, the judge made contingent findings on alternative interpretations of a PDD if she is wrong in her interpretation of the law (Article 3(10) of the Emissions Regulation 2007). If those contingent findings were accepted, then a majority of the sample cars would have an unlawful defeat device.
Nicola Boyle, Managing Partner, said:
“We support the points made by the lead solicitors, setting out the reasons around the appeal against Mercedes in the Nox litigation. Having considered the July judgment in detail, we, together with law firms acting for other claimant groups agreed that the judge’s definition of what constitutes a Prohibited Defeat Device is too narrow and that she has contradicted established EU law on what a defeat device is. It creates a divergence with much of Europe with England/Wales in danger of becoming the only place in Europe that allows manufacturers to build and sell cars containing these types of device which allow increased emissions levels.”
Background
The trial, which began in October 2025, was the largest group claim trial in English and Welsh legal history, involving the claims of 1.6 million drivers against 16 car manufacturers.
Due to the unprecedented scale of the Dieselgate claims, the High Court trial heard the test cases including against Mercedes and four other car manufacturers - the five “lead defendants” - ahead of the claims against other manufacturing groups.
Law firms Leigh Day and Pogust Goodhead are the joint lead solicitors working alongside 21 other law firms on behalf of the 1.6 million vehicle owners bringing a claim.
At the trial it was alleged that PDD software had been installed in vehicles’ emission control systems which reduced the effectiveness of the NOx controls in various normal driving conditions outside the type-approval test. It was argued that the cars’ emissions control systems were effectively ‘turned down’ when they were driven on the road because they reduced the vehicles’ fuel efficiency and performance, and the manufacturers were worried this would impact on vehicle sales.
