New Delhi, Oct. 29 -- As India moves to tighten its vehicle fuel-efficiency rules, a courtroom battle in the UK offers a cautionary tale. Carmakers including Mercedes-Benz, Ford, Renault, Nissan and Stellantis brands Peugeot and Citroen are facing a class-action lawsuit for allegedly using "defeat devices"-software that detects regulatory tests and temporarily suppresses emissions. The charges echo the 2015 Volkswagen "Dieselgate" scandal, when the German giant admitted to rigging diesel engines to cheat pollution tests.

Valued at about $8 billion, the case is among the largest consumer suits in UK history and is expected to conclude by mid-2026. Its outcome could shape how regulators worldwide design and enforce emission and efficiency ...