Lawyers representing 1.6 million vehicle owners are considering whether to seek permission to appeal following today's High Court judgment in the Dieselgate trial

For Ford, Renault and Nissan, the judge found that the defeat devices did not meet the definition of a PDD and therefore did not breach Emissions Regulations.

The judgment creates a significant divergence between the legal position in Great Britain and much of Europe. 

Key parts of the judgment 

In her judgment, Lady Justice Cockerill ruled that Peugeot/Citroen and Mercedes installed unlawful VW-style cycle recognition defeat devices in some of their vehicles, although she was not persuaded that the Mercedes defeat device made a difference to the levels of nitrogen oxides (NOx emissions) in practice in the particular test vehicle. 

However, the judge decided post-Brexit not to follow several key decisions of the Grand Chamber of the Court of Justice of the European Union (CJEU). This means that defeat devices that would be likely to be found to be illegal across the EU are allowed in Great Britain. 

The judge accepted that if she is wrong in her interpretation of the law (Article 3(10) of the Emissions Regulation 2007), then a majority of the sample cars would have an unlawful defeat device. 

In relation to Ford, the judge found that the devices alleged were not defeat devices, but noted that separate issues about serious defects in Ford’s Lean NOx Trap (LNT) emissions control equipment were not addressed in this trial. 

On behalf of Leigh Day’s Mercedes, Ford, Peugeot/Citroen, Renault and Nissan Claimants, Leigh Day’s senior partner Martyn Day said: 

"The High Court has found that despite their denials, other manufacturers also used VW-style defeat devices. The Judge has also found that many other defeat devices are lawful because she surprisingly disagreed with the established EU case law on what a defeat device is. 

"If this ruling is followed in Great Britain then this is now the only significant place in Europe where manufacturers are free to build and sell cars that contain these types of devices. 

"We welcome some of the Judge’s findings, but we think important parts of the decision are disappointing not least because of the impact on the environmental and consumer protection. We are considering with our clients whether to apply for permission to appeal."

On behalf of Pogust Goodhead’s Mercedes, Ford, Peugeot/Citroen, Renault and Nissan Claimants, Anna Varga said:  

"Today's judgment does not bring this litigation to an end. The Court has found that certain manufacturers installed unlawful defeat devices, but it also adopted a significantly narrower interpretation of the law than that applied elsewhere in Europe. It is that interpretation, and the important legal issues flowing from it, which will now require careful consideration.

"Our responsibility is unchanged. We represent 1.6 million motorists who are entitled to have their claims pursued with determination and rigour. We will continue working closely with our co-lead firms and leading counsel to assess the judgment, consider the appropriate next steps and ensure every properly arguable avenue remains available to our clients. 

"This litigation has always been about accountability. That principle has not changed today, and neither has our commitment to the people we represent."

Mercedes owner and Dieselgate claimant Richard Barnes said: 

"I am very disappointed by today’s judgment. The judge’s narrow decision regarding what is a defeat device seems to me is overly restrictive. I do not believe there should be different rules governing diesel emissions in England and Wales and the rest of Europe, and I would like to see this interpretation tested by the appeal courts."

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 14 car manufacturers. 

Due to the unprecedented scale of the Dieselgate claims, the trial heard the test cases against Mercedes, Ford, Renault, Nissan, and Peugeot/Citroen - designated by the High Court to be the five “lead defendants” - ahead of the claims against other manufacturing groups: Vauxhall/Opel, Volkswagen/Porsche, Jaguar Land Rover, BMW, FCA/Suzuki, Volvo, Hyundai-Kia, Toyota and Mazda.

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.

Lawyers for the claimants argued that the cars’ emissions control systems were being 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.

Law firm Leigh Day is one of the joint lead solicitors working alongside 21 other law firms on behalf of the 1.6 million vehicle owners bringing a claim.