If you own, or have owned, a diesel car, you have probably seen an advert, a social media post or a headline suggesting you could be owed compensation. The “diesel emissions scandal” – widely known as Dieselgate – has produced one of the largest group claims ever brought in England and Wales, and it is still working its way through the courts. This guide explains, in plain terms, what happened, what the courts have decided so far, and what owners should understand before deciding whether to join a claim.
What the diesel emissions scandal actually involved
The story began in the United States. In September 2015, the US Environmental Protection Agency (EPA) issued a notice of violation against Volkswagen, alleging that certain diesel cars contained software able to recognise when they were undergoing official emissions testing. Under test conditions the software switched full emissions controls on; during ordinary driving those controls were reduced. The EPA described the software as a “defeat device” and said it allowed nitrogen oxides (NOx) to be emitted at up to 40 times the permitted standard in the affected 2.0-litre models.
Volkswagen later admitted that the software had been fitted and that roughly 11 million vehicles worldwide, including around 1.2 million in the UK, were affected. The company subsequently reached large settlements in the US and Europe. In 2022 it settled the first major UK group claim, agreeing to pay £193 million to around 91,000 drivers in England and Wales, while making no admissions on liability, causation or loss.
What turned a single company’s problem into an industry-wide question was the research that preceded it. In 2013 and 2014, researchers working with the International Council on Clean Transportation (ICCT) measured real-world emissions from diesel cars and found NOx levels far above regulatory limits. Sharing those findings with regulators helped trigger the investigations that followed. The EPA publishes its own explanation of what a defeat device is and how the Volkswagen case was handled.
How a defeat device works
To understand the claims, it helps to know a little about how a modern diesel engine manages pollution. Diesel engines produce NOx, and manufacturers control it in two main ways: trapping it in a storage catalyst, or treating it with a urea-based solution often sold under names such as AdBlue. Both approaches add cost and can slightly affect fuel economy or performance, which is why the way the software manages them matters.
A defeat device, in regulatory language, is software or hardware that bypasses, defeats or renders inoperative a required element of the emissions control system. In the Volkswagen case, the EPA said the software could sense test conditions by monitoring factors such as vehicle speed, engine operation, air pressure and even the position of the steering wheel, then adjust the engine accordingly. The effect was a car that met limits in the laboratory while emitting more pollution on the road. The device is embedded in the engine control software, so it cannot simply be switched off by an owner.
Why NOx emissions matter
NOx is a group of gases linked to respiratory and cardiovascular problems, and it contributes to poor air quality in towns and cities. That is why regulators set limits for real-world driving as well as for laboratory tests. As the EPA notes, a single vehicle is not, by itself, a health threat – but collectively, vehicles emitting above the legal limit add to the pollution that people breathe. This public-health dimension is a large part of why the scandal attracted so much attention beyond the car industry.
How the UK claims developed
The UK litigation has unfolded in stages. The Volkswagen group claim ended in the 2022 settlement described above. A much larger case then followed, often called the Pan-NOx litigation. It involves claims from around 1.6 million vehicle owners against 14 manufacturer groups and is believed to be the largest group claim ever heard in England and Wales.
Because of the scale, the court selected five “lead defendants” to be tried first: Mercedes-Benz, Ford, Renault, Nissan, and Peugeot/Citroën. A 13-week trial began in October 2025 and examined a sample of around 20 vehicles built between roughly 2012 and 2018. The remaining manufacturer groups – including Vauxhall/Opel, Volkswagen/Porsche, Jaguar Land Rover, BMW, Volvo, Hyundai-Kia, Toyota and Mazda – are expected to be dealt with separately, using the lead judgment as a guide to how the law is likely to be applied.
What the July 2026 High Court ruling decided – and what it did not
On 10 July 2026, the High Court delivered its liability judgment. It found that, in the majority of instances examined, the technology at issue did not amount to a prohibited defeat device. It concluded that specific technology used in one Mercedes vehicle and two Peugeot/Citroën vehicles did meet the legal definition, while for Ford, Renault and Nissan the devices examined did not meet that definition. The ruling was widely reported, with manufacturers welcoming the outcome and claimant law firms indicating they were considering whether to seek permission to appeal.
Two points are worth being precise about. First, the judgment did not decide individual claims and did not award any compensation. It resolved preliminary legal and technical questions that will shape the wider litigation. Second, the judge chose, after Brexit, not to follow several rulings of the Court of Justice of the European Union on what counts as an illegal defeat device. Claimant lawyers argue that interpretation is narrower than the approach taken in much of Europe, and that if it were found to be wrong, more of the sample vehicles could be treated as having unlawful devices. That argument may be tested on appeal.
A further High Court hearing, currently scheduled for around October 2026, is expected to consider the consequences of the findings – including questions about remedies and how any damages might be calculated where breaches have been established. Until that stage is reached, the practical position for most claimants is unchanged.
Who may be able to claim
Eligibility is not universal, and it depends on the manufacturer, the vehicle and the law firm involved. Broadly, claims in the UK have generally concerned diesel cars and vans bought, leased or financed during a window that is often described as roughly 2007 to 2018, though the years and models vary between cases. Many claims do not require you to still own the vehicle, provided you have proof that you were the registered keeper.
Because the litigation has been running for years, several firms have closed their books to new claims against the lead defendants. Deadlines, vehicle lists and criteria can differ from one firm to the next, so the only reliable way to check is to contact a regulated solicitor directly and confirm the current position for your specific make, model and dates of ownership.
Timing also matters. Under the Limitation Act 1980, claims founded on tort or simple contract must generally be brought within six years of the date the cause of action accrued. There are recognised exceptions – for example where a claim is based on an allegation of deliberate concealment – but limitation is a technical area, and whether a particular claim is in time is a question for a lawyer, not a general guide.
How group claims are funded and how fees work
Most large consumer claims in England and Wales are not paid for upfront. They are typically run under arrangements such as a conditional fee agreement (“no win, no fee”) or a damages-based agreement. The mechanics vary, but the broad idea is that the firm’s fee becomes payable only in defined circumstances, often as a percentage of any compensation recovered. Claimants may also be asked to take out “after the event” insurance to cover the risk of paying the other side’s costs if the claim fails, and some policies are capped. These arrangements are regulated, and the exact terms differ between firms, so it is sensible to read the agreement carefully and ask what you would owe in each possible outcome before signing anything.
It also helps to understand that a group claim is a shared exercise. The firms coordinate on common legal issues, while individual claims still depend on the claimant’s own circumstances. Nothing about a fee arrangement should be read as a prediction of the result: whether a claim succeeds, and what it is worth, is decided by the evidence and the court, not by the way the fees are structured.
Documents and steps to gather before you file
If you are considering a claim, preparation is mostly about paperwork. Having the following to hand can make an initial assessment quicker and more accurate:
- Proof of purchase or lease, such as an invoice, receipt or finance agreement.
- Registration details and, if available, the V5C logbook information.
- Service history and any recall or software-update records.
- The make, model, engine size and year of manufacture.
- Dates you owned the vehicle and whether you were the registered keeper.
- A note of any correspondence you have already had with a manufacturer or law firm.
Keeping these records is worthwhile even if you decide not to proceed now: in a long-running group claim, the ability to prove the age, model and history of your vehicle can matter later on.
What a claim could be worth
No one can reliably promise a figure. Compensation is not automatic, and the UK litigation against most manufacturers is still at the stage of deciding liability and, for some vehicles, remedies. Commentators have cited figures in the low thousands for individual claimants, but those are estimates rather than guarantees, and the amount any person receives – if anything – will depend on the findings in their case, the manufacturer involved and the terms of any settlement or judgment. Treat any fixed number you see in an advertisement or on social media with caution.
Staying informed and choosing representation
There are hundreds of firms and claims-management services competing for diesel claims, and they are not all the same. Before signing up, check that a firm is regulated, ask who will actually handle your case, request the fee agreement and any insurance terms in writing, and keep copies of everything. It can also help to follow independent journalism on the legal services sector as a whole; recent coverage of a UK law firm is one example of the kind of reporting that is available to consumers weighing their options.
Frequently asked questions
Do I need to still own the car to make a claim?
Generally, no. Many claims have been brought by people who no longer own the vehicle, provided they can show they were the registered keeper and can supply proof of purchase or lease. The requirement is evidence of ownership or use during the relevant period, not current ownership.
Is compensation guaranteed if a manufacturer is found to have used a defeat device?
No. A finding of liability does not automatically produce a payment, and the court has not yet decided how damages would be calculated in this litigation. Compensation depends on the specific findings, the individual claim and any settlement or judgment.
How long will a claim take?
It is difficult to give a firm answer. The lead trial concluded in July 2026, a further hearing on consequences is expected around October 2026, and appeals are being considered. Claims against the remaining manufacturer groups have yet to be heard. Realistically, many observers expect resolution to run well past 2026, but every case and jurisdiction is different.
What happens if I have already joined a claim?
If you are already represented, you usually do not need to take any immediate action. Your solicitors will review the judgment and contact you with next steps. Keeping your paperwork safe and responding to requests from your legal team remains the most useful thing you can do.
Can I make a claim on my own without a solicitor?
In theory an individual can bring a claim in the courts, but emissions cases involve complex technical and legal issues, and the lead litigation is a large coordinated group action. Most owners participate through a regulated firm. If you are unsure, a short initial conversation with a solicitor is generally the most efficient way to understand your position.
How this article was put together
This guide draws on publicly available material from regulators, courts and reputable news reporting, including the US Environmental Protection Agency’s pages on the Volkswagen violations, the International Council on Clean Transportation’s account of the research that preceded the scandal, reporting on the 2022 UK settlement and the July 2026 High Court judgment, and the text of the Limitation Act 1980. Figures and rulings reflect the position as reported in 2026. Because the litigation is ongoing and deadlines and eligibility criteria vary by manufacturer and law firm, readers should confirm current details with a regulated solicitor before acting. This article is general information and is not legal advice.
