The ‘Dieselgate 2’ High Court case

‘Dieselgate 2’ is the UK’s largest-ever class action. It was launched by 1.6 million members of the British public against numerous carmakers who fitted diesel vehicles with software (‘defeat devices’) that resulted in much higher real-world nitrogen-oxide (NOₓ) emissions than those shown in laboratory tests. The High Court trial, which began on 13 October 2025, focuses on a representative sample of vehicles from four major manufacturers including Mercedes, Ford, Nissan/Renault and Peugeot/Citroën (Stellantis). If liability is established, the damages exposure has been estimated in the region of £6 billion.

The current litigation builds directly on the fallout from the original 2015 Volkswagen “Dieselgate” scandal, when VW admitted using defeat-device software to pass emissions tests while allowing far higher emissions in normal driving. That scandal led to a settlement of just under £200 million for 91,000 consumers and established the legal framework for what might constitute a “prohibited defeat device.” However, despite this verdict, it has become apparent over the last few years that other car manufacturers have used defeat devices— something that will now be tested in court.

Countless members of the British public, including young children, have been harmed by breathing excess emissions from diesel vehicles suspected of using prohibited defeat devices. Research conducted earlier this year by the Centre Research on Energy and Clean Air (CREA) revealed that as a result of just the excess emissions (not the total emissions) from the installation of defeat devices in UK vehicles:

* Approximately 16,000 people have already died as a result of excess emissions

* A further 6,000 premature deaths will occur in coming years without action

* Excess emissions have caused 30,000 cases of asthma in children

* In the UK alone, these excess emissions had led to 800,000 days of sick leave 

* The total economic burden due to deaths and poor health was £96bn by 2024

London remains the UK’s primary hotspot for air pollution with diesel vehicles responsible for around 95% of NOₓ emissions. However, major improvements have been achieved thanks mainly to the Ultra Low Emissions Zone (ULEZ) which has seen average roadside NO₂ levels roughly 27% lower than they would have been. Health data from Imperial College London linked poor air quality to over 1,700 hospital admissions for asthma and serious lung conditions between 2017–2019, including about 700 child asthma admissions. London now meets UK legal limits for NO₂ in most areas, but still exceeds WHO guideline values, meaning health risks remain.

But it is not just London that is badly impacted. The North West, for instance, continues to face some of the highest respiratory disease burdens in the UK, driven in part by traffic-related pollution, with areas like Salford and Liverpool recording high emergency hospital admission rates for lung diseases. The UK’s current average PM₂.₅ concentration (fine particulate matter) is approximately 7.4 µg/m³, while in Leeds urban background PM₂.₅ is around 8 µg/m³, with some sites in South Yorkshire exceeding 10 µg/m³.

Four companies (Mercedes, Ford, Nissan/Renault and Peugeot/Citroën) were chosen by the court as lead defendants to be tried first as the case is so big, with 20 diesel models forming the sample for scrutiny. Depending on the outcome of this case, nine other carmakers are facing similar claims.

Data based on the claimant pool indicate that close to 90 percent of these cars are likely to have defeat devices. Under real driving conditions, some cars exceed the legal limit by 20 or 30 times, with the Renault Kangoo the worst offender at almost thirty three times the legal limit. Surprisingly, in many instances the newest models are the worst offenders.

The Pan-NOx trial before Lady Justice Cockerill in the High Court started on 13 October, and will examine whether major carmakers used illegal “defeat devices” to cheat NOx emissions tests, misleading consumers and increasing pollution across Europe.

So far, the court has heard opening statements from all parties and expert witnesses including allegations that the auto manufacturers prioritised profit over compliance, with Ford and Nissan/Renault using “purging” mechanisms, Stellantis deploying multiple cheats, and Mercedes creating complex systems to hide similar practices, while only making voluntary updates.

Thomas De La Mare KC, lead counsel for the claimants, described the carmakers’ approach as being that “we would rather cheat than comply with the law.” The trial continues with factual evidence focused on each manufacturer, beginning with Mercedes, lasting until the end of the year and a verdict unlikely before next Summer.

The Government does not need to wait for the result of this long and complex case to act. It already has a trump card that can ensure that the companies are held accountable under the law. Earlier this year, the Department for Transport (DfT) launched an investigation into the possible use of defeat devices, involving many of the same brands represented in the trial. Unfortunately, to date there has been little indication of any progress in that investigation. Every month that the results are delayed puts more people—including children—at risk for asthma and other health issues.

The government should make clear that it is prepared to act now. Since 2024, the Environment Act has enabled the government to introduce regulations that would require manufacturers to recall cars when there are reasonable grounds to believe they do not meet applicable environmental standards. The government should move now to put those regulations in place, so that any use of defeat devices can be corrected promptly at the companies’ expense.

For too long, auto manufacturers in the UK have victimised the public. They have misled consumers about the pollution emitted by diesel auto engines and have put millions of citizens at risk simply because they live or work near roads.  These companies should step forward and make things right with those they have harmed. And, the government should do everything it can to ensure that happens. We should not have to wait for Dieselgate 3.