Volkswagen AG is facing one of the largest-ever U.K. class action lawsuits, with almost 100,000 vehicle owners accusing it of misleading them by installing emissions-cheating software that made it appear their diesel vehicles met environmental standards.

Lawyers for the drivers opened their case Monday, and must first prove that the allegations belong in court. They need judges to follow findings by regulators that led to vehicle recalls, and to rule that the software is a so-called defeat device that’s banned under European law. Then the case would proceed to another trial to decide whether the owners lost anything from buying the vehicles.

The automaker has faced numerous lawsuits after the use of the software designed to lower emissions when being tested was exposed by a U.S. probe in 2015. That led to a recall throughout Europe that cost the company 29 billion euros ($32 billion). Regulators in the Netherlands and Italy have fined VW for use of the software, while a German probe last year fined the carmaker 1 billion euros.

In its court filing, VW says that the law only prohibits devices that reduce the effectiveness of pollution control systems and not those, like the software, which enhance them. According to the driver’s lawyers, that argument is an abuse of the intention of the law.

“The defendants’ case results in an understanding of the defeat device that is entirely divorced from the emissions test and the emissions limits,” Tom De La Mare, an attorney for the drivers, said in court. “It’s aimed at legitimizing the total subversion of the emission regime.”

In his submissions, De La Mare pointed to an diagram from an internal VW document, showing how the software made the vehicle sacrifice its fuel consumption, driveability and engine noise when under testing, in order to dip beneath the legal limit on pollutants.

A spokesman for Volkswagen said that the drivers didn’t suffer any losses and that the vehicles didn’t use prohibited defeat devices. The company also disputes the number of claimants involved in the class action, saying it’s closer to 85,000.

Gareth Pope, a lawyer from Slater and Gordon representing the drivers, said in a statement that VW had perpetrated an “environmental scandal” and had spent “millions of pounds denying the claims our clients bring.”

Many similar cases are proceeding in German courts, including a group action that involves thousands of Volkswagen drivers. They argue that they faced their vehicles being banned from the road and suffered losses as the resale value of their cars declined. Those cases hinge on whether the fact that a software update that made the cars legal to use invalidates the claim.

VW in Germany has for years argued that the software used here was legal. That argument was tossed by Germany’s top civil court in February in a rare a rebuke of VW’s position.

An earlier version of this story was corrected to reference to regulator fine in third paragraph.

(Updates with detail on software in seventh paragraph)

–With assistance from Karin Matussek.