Automakers deny wrongdoing, while the case highlights ongoing regulatory and reputational risks a decade after Volkswagen's dieselgate scandal.

Some of the world's largest automakers face a landmark trial Monday in London's High Court, accused of using illegal "defeat devices" to bypass diesel emissions regulations, a decade after Volkswagen's dieselgate scandal.

Lawyers representing 1.6 million vehicle owners allege that Mercedes-Benz, Ford, Nissan, Renault, and Stellantis-owned Peugeot and Citroen installed technology that detected when vehicles were undergoing emissions testing and adjusted performance to meet legal limits. On the road, the systems reportedly allowed the cars to emit pollutants above permitted levels.

The trial focuses on a sample of 850,000 vehicles. Any damages awarded will be decided in a separate hearing next year. A ruling could also influence hundreds of thousands of related claims against other automakers, including Stellantis-owned Vauxhall/Opel and BMW, making it one of the largest mass lawsuits in English legal history.

However, manufacturers deny wrongdoing, insisting their emissions control systems were legally and technically justified. Mercedes-Benz called the allegations "fundamentally flawed" and said the claims bear little resemblance to Volkswagen's 2015 scandal, which cost the German automaker more than 32 billion euros ($37 billion) in fines, vehicle refits, and legal costs.

Notably, the current case involves 14 manufacturers and has been valued at roughly 6 billion pounds ($7.97 billion) by claimants' lawyers. Similar lawsuits have also been filed around the world, including in the Netherlands, where a court found Stellantis diesel vehicles contained defeat devices, which Stellantis disputed. U.S. automakers have also faced fines and settlements related to diesel emissions compliance.

Legal experts and industry observers say the trial could set a precedent for emissions-related litigation worldwide, highlighting the persistent regulatory and reputational risks for automakers a decade after "dieselgate."

UK diesel emissions lawsuit targets top automakers