Did carmakers cheat the system? Landmark ‘dieselgate’ trial begins
October 13, 2025 by Siobhan Doyle
Car changing is a big deal
A massive court case has begun against six major carmakers accused of using “cheat” software to fake emissions results – and 1.6 million UK drivers could be affected.
A major High Court case kicks off this week. It accuses six carmakers – Mercedes, Ford, Peugeot, Citroen, Renault, and Nissan – of cheating emissions tests by using secret software to make their diesel cars appear cleaner than they really are.
Lawyers say this could become the largest class action in English and Welsh history. What’s more is that up to 1.6 million car owners might be involved.
The case stems from the global “Dieselgate” scandal first uncovered in 2015. Here, the US Environmental Protection Agency found Volkswagen had installed so-called “defeat devices” in millions of diesel cars. The software could detect when a car was being tested and reduce engine performance to produce artificially low emissions readings.
In the UK, Volkswagen settled a class action in 2022, splitting £193m between around 91,000 motorists. Globally, the company’s total bill has topped €32bn (£27.8bn) in fines, compensation, and legal costs.
Now, the High Court will determine whether the six new defendants used similar tactics – and whether their cars also breached emissions standards.
What could happen?
If the court finds against the carmakers, a second trial will determine how much compensation drivers could receive. A judgment isn’t expected until summer 2026, with potential payouts following later that year.
“A decade after Dieselgate, UK motorists finally have the chance to find out whether their vehicles contained tech designed to cheat emissions tests,” said Martyn Day, senior partner at law firm Leigh Day. “If proven, this would represent one of the biggest corporate trust breaches in modern times.”
All five carmakers have strongly denied the allegations. A Mercedes spokesperson said its test systems were “technically and legally justified,” while Renault, Peugeot, Citroen, Ford, and Nissan each said their vehicles complied with the regulations in place at the time.
What does this mean for you?
If the High Court rules against the carmakers, it could open the door for hundreds of thousands of UK drivers to claim compensation. Some experts think it could potentially be similar to the Volkswagen settlement.
Even if you’re not part of the current case, the outcome could shape how emissions claims and consumer rights are handled in the future. It may also influence how manufacturers market “eco-friendly” vehicles and how regulators enforce clean air laws.
Drivers who owned affected diesel vehicles between roughly 2009 and 2020 could eventually see payouts – or at least greater transparency – about how clean their cars really are.
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