Pan Nox the Series

What the Pan-NOx Judgment Actually Decided

A primary-source explainer: no framing, just what the court held

Written by Will Whawell. Human intelligence throughout; AI assisted with the drafting.

July 2026

On 10 July 2026 the High Court handed down judgment following the liability issues trial in the Pan-NOx Emissions Group Litigation — the largest group action in English legal history. Around 1.6 million claimants, proceeding under Group Litigation Orders, alleged that diesel vehicles made by the lead defendant manufacturers — Mercedes-Benz among them, alongside Ford, Renault-Nissan and Peugeot-Citroën — contained prohibited defeat devices: software that kept NOx emissions low during official regulatory tests while permitting higher emissions on the road. Cockerill LJ, sitting as a High Court judge, heard the liability trial between October 2025 and March 2026 (judiciary summary; Fountain Court).

The judgment turned on a question of construction: what counts as a prohibited defeat device under the Euro 5 and Euro 6b Emissions Regulation? The court adopted a narrow answer. A defeat device is one that detects a regulatory emissions test and objectively operates with the purpose of causing the emissions control system to work more effectively during the test cycle than it would on the road. Two elements matter: detection of the test, and that test-favouring purpose. Showing that a calibration strategy reduced the effectiveness of emissions control in real-world conditions was not, by itself, enough.

Applying that test, the claimants lost on the vast majority of their allegations. Most of the challenged calibration strategies were found to serve legitimate engineering purposes — component protection, thermal management and the like — and so fell outside the prohibition altogether. In reaching that construction the court declined to follow certain post-IPCD authorities of the Court of Justice of the European Union, considering that aspects of the CJEU's reasoning contained errors and that the English court had far better access to the detailed factual and expert evidence.

Two limited adverse findings survived. Against Mercedes-Benz, a coolant temperature setpoint functionality present in certain sample vehicles was found to be a prohibited defeat device — a functionality the company had removed by a software update rolled out in December 2015, with the court noting the post-update compliance of the sample vehicles. Against Peugeot-Citroën, a split-injection strategy in certain Euro 5 vehicles was likewise found prohibited.

What happens next: a damages and remedies trial is listed for October 2026 to determine what consequences, if any, flow from the limited findings that were upheld. Claimant lawyers have indicated they are considering appeal routes, particularly on the divergence from European case law. The manufacturers continue to deny systemic wrongdoing, and Mercedes-Benz has said it largely welcomes the ruling while reserving its position on the single adverse point.

Everything else written about this case — including the rest of this series — is interpretation built on those facts. This piece is the factual base; the commentary starts in Part 2.