Mishcon de Reya acts for campaign groups in call for open justice

The Dieselgate Litigation is one of the largest group actions to come before the English courts, with approximately 1.6 million car owners taking legal action against car manufacturers, including Mercedes-Benz, Ford, Nissan, Renault and Peugeot-Citroen, for allegedly using prohibited emissions "defeat devices" in their cars. Vehicle owners allege that these devices artificially lowered nitrogen oxide (NOx) emissions in test conditions, only for the vehicles to emit in excess of the legal NOx level when being driven on the road.
In documents ﬁled with the High Court ahead of a trial in October, the automotive manufacturers have redacted information about how and when the alleged defeat devices are said to operate.
The community interest group Mums for Lungs and environmental law organisation ClientEarth are asking the Court at this next hearing on 7 July to remove the redactions applied by the automotive manufacturers and to make the unredacted documents available to third parties on public interest grounds.
In May of this year, almost a decade since Dieselgate was uncovered, a German regional court convicted four former Volkswagen managers of fraud in connection with the Dieselgate scandal.

The High Court of Justice has set a hearing for 7 to 9 July 2025, where the Court will consider what conﬁdentiality restrictions should remain in place at the October 2025 trial. Mums for Lungs and ClientEarth, who are not parties to the litigation and do not stand to gain from any compensation if the vehicle owners are successful, will be making submissions at this hearing on the principle of open justice.

The Dieselgate Litigation is a major group action with approximately 1.6 million car owners taking legal action against vehicle manufacturers, including Mercedes-Benz, Ford, Nissan, Renault and Peugeot-Citroen, for allegedly using illegal “defeat devices" to manipulate emissions, in violation of UK and EU regulations. Defeat devices aﬀect the operation of an engine's emissions control system, switching it oﬀ or reducing its eﬀectiveness under certain conditions. This means that in the real world, vehicles with defeat devices can emit levels of NOx that far exceed regulatory limits. The total damages sought by the vehicle owners in the litigation exceed £6 billion.

In February 2025, Mums for Lungs wrote an open letter to the High Court of Justice, requesting that documents in the litigation be made publicly available due to the high level of public interest in this case and impact on human health. This letter was signed by over 650 signatories.

Mums for Lungs and ClientEarth each made an application ahead of the 7 July hearing asking the Court to remove all redactions to the legal documents setting out the parties' arguments on speciﬁc sample vehicles ﬁled in Pan-NOx proceedings.

The organisations believe that the heavily redacted materials include information relating to how the emissions control devices operate, such as the temperature, speed and torque thresholds at which they are alleged to artiﬁcially limit NOx emissions. As a result, the circumstances in which NOx emissions may be many times over the legal safety limits, have been kept secret.

Outside of this claim, ClientEarth sent complaints to the UK Government in Spring 2023. Since then, the Government has launched investigations into the suspected use of illegal defeat device technology. If such devices are found, the government must require corrective action by the responsible manufacturer, which could include recalls to ﬁx the problem – the rules are clear that vehicle owners should not bear the costs of this. However, these investigations are being hindered by delays and a lack of transparency. ClientEarth believes that making the key information in the litigation public will help to accelerate the government’s work to ensure that manufacturers clean up any vehicle found to have an illegal defeat device.

The intervention by Mums for Lungs and ClientEarth seeks to bring an important public health issue to light, as there is a well-documented connection between nitrogen dioxide, the harmful component of the NOx emissions, and adverse health impacts. Children are particularly vulnerable to the eﬀects of exposure to air pollutants due to their higher respiratory rates and less developed respiratory systems. A recent report commissioned by ClientEarth concluded that between 2009 and 2040 across the EU and UK excess NOx emissions will cause 205,000 premature deaths, 152,000 new cases of asthma in children, €1.2 trillion in economic costs and 24 million days of sick leave.

The outcome of the 7 July hearing will signiﬁcantly shape the October 2025 trial, which will determine whether the vehicles were ﬁtted with illegal defeat devices. If the redactions are allowed to remain, the claimants allege that much of this trial is likely to be conducted behind closed doors. Currently, redactions applied to publicly available Court documents omit key technical details about how the alleged defeat devices are said to work and whether they are operational during normal driving in the UK. If the circumstances in which any defeat devices operate mean NOx emissions are higher in normal driving conditions, they will have had a profound impact on public health.

Jemima Hartshorn, Founder and Director of Mums for Lungs, said: "The impact of air pollution on people’s health remains a live and urgent issue. Emissions from diesel cars are a major contributor to air pollution. Recent research suggests that excess emissions from cars allegedly ﬁtted with illegal defeat devices have caused asthma in children, pre-term and low weight births as well as thousands of premature deaths. The public should have access to information about the level of toxic pollution produced by diesel cars. We need transparency in order to ensure real accountability in the upcoming October trial, so that we can ﬁnally protect our children’s health."

Andrea Lee, campaigner at ClientEarth, said: “The scale of harm caused by unlawful and unsafe diesel emissions demands transparency from the auto manufacturers. It is deeply concerning that vital information about the operation of the alleged defeat devices continues to be kept hidden from the public. The public have a right to know the full extent of the suspected wrongdoing and the impact of these cars on the air that we all breathe. Greater transparency at the trial will shine a light on whether the vehicles were ﬁtted with illegal defeat device and help guide government investigations to urgently clean up any vehicles with defeat devices.”

Shazia Yamin, Partner at Mishcon de Reya, who is acting for Mums for Lungs and ClientEarth in these proceedings, said: “The outcome of the upcoming hearing will deﬁne the way this litigation is conducted and has implications for future Dieselgate proceedings. Our clients are making their applications to promote open justice because there is signiﬁcant public interest in this case. This litigation raises questions about public health, environmental responsibility, corporate governance and, most importantly, corporate accountability. Our clients are seeking to bring into the open important information that aﬀects us all. We look forward to the hearing and ﬁnding out whether unredacted public access to the parties’ sample vehicle statements of case will be granted.”