High Court hands down important judgment on the open justice principle in the Dieselgate proceedings

The Dieselgate litigation, which is brought as a group action by approximately 1.6 million car owners, concerns car manufacturers’ alleged use of prohibited “defeat devices” to mask the extent of cars’ nitrogen oxide (NOx) pollution. The total damages sought by car owners is estimated to exceed £6 billion.

At a hearing on 7 to 9 July, two environmental NGOs – Mums for Lungs and ClientEarth – applied for unrestricted access to certain documents filed in the proceedings so that they, and the public more generally, could understand how prohibited defeat devices operate and their environmental and health impacts. The defendant car manufacturers sought to maintain the confidentiality restrictions that applied to the documents.

On 25 July 2025, Constable J handed down judgment: Various Claimants v Mercedez-Benz & Ors [2025] EWHC 1931 (KB). Constable J granted Mums for Lungs’ and ClientEarth’s applications in full and ordered the relevant documents to be made publicly available in unredacted form: see paras 21, 24 to 62.

Tim Buley KC and Barney McCay acted for Mums for Lungs and ClientEarth. They were instructed by Shazia Yamin, Frances Beddow and Destiny Okongwu of Mishcon de Reya.

A fuller summary of the judgment and its consequences can be found on Mishcon de Reya’s website here.