Diesel Owners in Portugal Could Win Payouts as London Court Rules on Emissions Fraud

The London High Court will resume closing arguments between 2 and 20 March 2026 in what has become the largest consumer class action in British legal history, a case involving approximately 1.6 million UK drivers challenging major manufacturers over alleged emissions fraud. The decision, expected in July 2026, will determine whether defendants installed prohibited defeat devices. If liability is established, a separate damages trial scheduled for October 2026 will determine compensation amounts.

Why This Matters

• Pan-European precedent: Nine additional automakers, including BMW, Toyota, Volkswagen, and Jaguar Land Rover, will be bound by the July ruling, even though they are not named defendants in this phase.

• Portugal exposure: Many of these same brands — Mercedes, Renault, Nissan, Peugeot, Citroën, DS — dominate Portugal's diesel fleet, meaning similar class actions could follow if UK liability is confirmed.

• Criminal trials pending: France has scheduled proceedings against major manufacturers on fraud charges; Germany's Federal Court is also hearing climate-liability cases targeting automakers.

• Regulatory credibility: The case tests whether EU environmental law has teeth when national regulators fail to act — a question that concerns anyone living under Brussels-backed air-quality rules.

What Diesel Owners Need to Know

The claims allege that defeat devices — software or hardware calibrations — allowed vehicles to pass lab emissions tests while pumping out nitrogen oxide (NOx) levels several times higher in real-world driving. These systems were allegedly programmed to detect test conditions and temporarily optimize performance, then revert to higher-polluting modes on public roads.

Named defendants in the London action include:

• Mercedes-Benz Group

• Ford Motor Company

• Renault and Nissan Motor Co.

• Stellantis brands: Peugeot, Citroën, DS

All deny wrongdoing, arguing that their emissions-control systems are calibrated for performance and safety across varied driving conditions and that no intentional fraud occurred. Legal teams contend that their systems differ fundamentally from the original Volkswagen scandal, in which the German manufacturer admitted to installing illicit software in 11 million cars worldwide.

The European Court of Justice has previously addressed related liability questions, establishing that manufacturers can face liability even when vehicles received type-approval from national authorities. Legal precedent indicates that damages awards may be calculated as a percentage of the vehicle purchase price, though exact figures depend on individual case determinations.

The Volkswagen Precedent

Volkswagen's 2015 admission triggered the Dieselgate scandal and has resulted in billions in fines and settlements globally. In the UK, Volkswagen agreed in 2022 to pay compensation to affected British drivers — a deal brokered by law firm Pogust Goodhead, which is also representing claimants in the current London trial.

That settlement established a per-vehicle payout benchmark that helped inform compensation calculations in similar cases. If the London court finds Mercedes, Ford, Renault, Nissan, and Stellantis liable on similar grounds, the October 2026 damages phase will likely reference those precedents as a starting point.

What This Means for Portugal Residents

Important clarification: This is a UK trial and does not automatically entitle Portugal residents to compensation. However, the implications ripple into Portugal:

Fleet overlap: Diesel vehicles from the named manufacturers — particularly Renault, Peugeot, Citroën, Mercedes, and Ford — represent a substantial share of Portugal's passenger-car fleet, especially those registered between 2009 and 2019.

Parallel litigation risk: A UK liability finding would strengthen the evidentiary foundation for Portuguese consumer-protection groups or environmental NGOs to launch similar class actions under Portugal's Consumer Defence Law (Law 24/96). However, Portugal residents would need to pursue separate legal action through Portuguese courts.

Resale-value concerns: If brands are found liable, secondary-market prices for affected diesel models may fluctuate as buyers factor in potential future recalls, retrofits, or disclosure obligations.

Emissions-zone enforcement: Portuguese cities, including Lisbon and Porto, have introduced or expanded low-emission zones (ZER – Zona de Emissões Reduzidas). Vehicles found to have defeat devices could face reclassification or higher access fees.

Tax clarification: Portugal's Imposto Único de Circulação (IUC) and Imposto sobre Veículos (ISV) calculations depend on emissions certifications. While hypothetically a finding could affect certifications, no such tax recalculation mechanism currently exists in Portuguese law, so readers should not expect retrospective tax adjustments.

The Broader European Context

Dieselgate-related litigation is ongoing across the continent:

• Netherlands: A Dutch court ruled in 2024 that certain vehicle models used software questioned as non-compliant.

• Spain and Italy: Consumer-protection agencies have opened investigations into several brands.

• Belgium: Class-action law reforms have enabled groups of diesel owners to file consolidated claims.

The European Commission has initiated enforcement actions emphasizing that national regulators must enforce environmental law.

Timeline and Next Steps

• 2–20 March 2026: Closing arguments conclude in London.

• July 2026: High Court issues liability judgment.

• October 2026: If liability is established, trial begins to quantify damages.

Should the court rule against the manufacturers, appeals are likely, potentially extending resolution into 2027 or 2028.

What Diesel Owners Should Do Now

If you own or previously owned a diesel vehicle manufactured by Mercedes, Ford, Renault, Nissan, Peugeot, Citroën, or DS between 2009 and 2019, monitor the July judgment closely.

Portugal residents: Watch for announcements from Portuguese consumer-protection organizations (such as DECO – Associação Portuguesa para a Defesa do Consumidor) regarding potential class actions in Portugal. If the London court rules against manufacturers, these organizations may pursue similar claims in Portuguese courts on behalf of local residents.

General steps:

• Document ownership: Preserve purchase invoices, registration certificates, and maintenance records.

• Monitor for updates: Track announcements from consumer-protection groups and legal firms specializing in automotive claims.

• Verify your vehicle: Not all models or engine codes may be affected; check your Vehicle Identification Number against published lists once court findings are released.

• Consider resale timing: Consult with consumer advisors about timing if you plan to sell your vehicle.

The London trial represents a significant moment for automotive environmental enforcement. With the March 2026 closing arguments approaching, the outcome could establish important legal precedent across Europe and potentially trigger similar consumer actions in Portugal and other jurisdictions.