The Court's judgment followed a hearing on 7 to 9 July 2025, at which Mums for Lungs and ClientEarth argued that unredacted copies of the legal documents detailing the operational parameters of alleged defeat devices in the diesel vehicles should be made available to the public. These defeat devices are said to affect the operation of an engine's emissions control system, switching it off or reducing its effectiveness under certain conditions, in contravention of UK and EU regulations.
As a result of the Court's decision, any information about how the alleged defeat devices operate can now be discussed in open court at the trial in October. In the meantime, unredacted copies of the parties' statements of case will be uploaded to a Sharepoint site, which members of the public can request access to by writing to the Court.
In his judgment, Mr Justice Constable accepted the campaign groups' arguments that the redacted information was crucial to the public's understanding of the issues in dispute and that this outweighed the supposed commercial sensitivity of the information. He went on to find that the vehicle manufacturers had "failed to establish at any level of specificity that there is any meaningful confidentiality remaining in the parameters, values and engineering strategies given the passage of time, regulatory change and obsolescence." Accordingly, there was no justification for retaining the redactions and giving the manufacturers "the benefit of a cloak of confidentiality" which "would have the effect of disabling the public from understanding the issues in dispute".
Barney McCay, barrister for the two campaign groups, told the Court that the effect of the redactions was "to keep secret allegations that go to the heart of the proceedings" and that denying the public access to these allegations would be contrary to the principle of open justice. Mr McCay also explained that access to the material could not be delayed until after a judgment in the main proceedings because "air quality issues are being talked about now, they're the subject of legislation that's going through Parliament now, and they're causing anxiety for parents whose children are affected by air-quality-related health issues now".
Letters in support of ClientEarth and Mums for Lungs were provided by media and charity organisations, namely Reuters, The Financial Times, Asthma + Lung UK, The Ella Roberta Foundation, T&E UK, and German environmental organisation, Deutsche Umwelthilfe. Mums for Lungs put evidence before the Court about the devastating impact that air pollution from vehicle emissions can have on public health, especially on children who are particularly vulnerable to the effects of exposure to air pollutants due to their higher respiratory rates and less developed respiratory systems. Mums for Lungs also shared the results of a recent survey they conducted, which illustrates public concern and awareness of the potentially harmful effects of air pollution. For instance, of the 318 respondents to the survey, 94% reported that they had taken direct action in response to pollution concerns, from taking their children out of school on days with poor air quality, to avoiding congested roads, to regularly checking local pollution levels.
Both campaign groups gave evidence about a recent study commissioned by ClientEarth, which found that excess emissions from the likely use of defeat devices are projected to cause 205,000 premature deaths and 152,000 new cases of asthma in children across the UK and EU between 2009 and 2040.
ClientEarth also provided evidence to the Court about the ongoing investigations by the Department for Transport (DfT) and other regulators into diesel vehicles suspected to contain illegal defeat devices.
According to case law, one of the circumstances in which regulators should conclude that a defeat device is illegal is if it means emissions regulation systems are less effective (or turned off altogether) in normal driving conditions during most of the year. The DfT must take corrective action if it finds any illegal defeat devices, which can include recalls of affected vehicles. To date, ClientEarth has provided evidence about suspicious vehicles to regulators in an attempt to ensure that these investigations are "robust, sufficiently wide in scope and carried out with due urgency". If the allegations in these proceedings indicate that the defeat devices may have operated during normal driving for most of the year in the UK, ClientEarth will ask the DfT to consider this information as part of its investigation.
Jemima Hartshorn, Founder of Mums for Lungs, commented: “We are delighted with this outcome. The judge cut to the heart of the issue: we all have a right to understand which car manufacturers are alleged to have produced cars that are the most polluting; with millions of them still driving on
our roads and potentially making our children sick, every breath they take. We are now one step closer to holding these companies to account and hope the government will finally take steps to prioritise children’s health.”
ClientEarth lawyer Emily Kearsey said: “Almost ten years after the Dieselgate scandal first broke out, we’re finally going to uncover key information that car manufacturers have refused to disclose. People have a right to know the full scale of the suspected wrongdoing – this judgment will finally shine a light on the extent of the allegations. But that's not the only win. Having access to these documents will also help drive urgent government action to track down excessively polluting cars still on the road today and order the responsible manufacturers to fix them. Today's ruling is another crucial step towards cleaner air, better health and real accountability.”
Shazia Yamin, Partner at Mishcon de Reya, said: “The applications by our clients, Mums for Lungs and ClientEarth, raise important points of legal principle on issues that matter to us all and we are pleased they have been successful in full. In reaching his decision, the judge has carefully considered the evidence from our clients about the strong public interest in these proceedings and weighed this against arguments of supposed commercial sensitivity advanced by the vehicle manufacturers. This judgment sets a clear precedent that companies cannot simply rely on assertions of confidentiality to keep allegations against them secret.”