A proposed multi-billion pound British class action against Google, which alleges the internet giant secretly tracked millions of iPhone users, is not viable and should not be allowed to proceed, the Supreme Court was told on Wednesday.

Antony White, a lawyer for Google, told the first day of a two-day hearing that any maiden, U.S.-style data protection lawsuit could only seek redress under English laws if a data breach led to claimants suffering damage.

“It is not my case that loss of personal data may not have serious consequences, but it may not always do so in a way that attracts compensation,” he said, adding that any uniform award would also fail to take into account differing phone usage.

Richard Lloyd, former director of consumer rights group Which?, is leading the landmark claim that seeks to extend Britain’s fledgling class action regime and could set the scene for vast, similar data protection claims against tech giants such as Facebook, TikTok and YouTube.

The case, brought on behalf of more than five million Apple iPhone users, hinges on what damages can be recovered by consumers for data breaches and whether class actions can be used to claim them.

Lloyd, who says he wants to hold the world’s biggest companies to account, has estimated that people who used iPhones between 2011 and 2012 could be owned redress of more than 3 billion pounds ($4.2 billion) if any future trial succeeds.

He alleges that Google illegally took iPhone users’ personal data by tracking internet browsing histories and used this to sell a lucrative, targeted advertising service.

“Google makes billions of pounds in revenue from advertising based on our personal data every year,” he said in a statement. “It is only right that they should be held to account for profiting from the misuse of that personal data.”

Experts say the case is “hugely significant” and urge businesses to be fair and transparent when harvesting and using troves of personal data for commercial gain.

“If the judgment goes in favor of the claimants, we will see the floodgates open to a tsunami of representative data class actions in the UK,” said Julian Copeman, a partner at Herbert Smith Freehills.

Critics of “opt out” class actions, which automatically bind a defined group into a lawsuit unless individuals opt out, say they can lead to claims without merit and lush profits for litigators and their funders.

Proponents say they allow easier access to justice, especially when individual claims are too small to pursue individually, and that alternative “opt in” lawsuits, where every claimant signs up, are costly and time-consuming.

The Confederation of British Industry, a trade body, says such cases could be “highly detrimental,” noting the risk of ruinous damages awards could prompt settlements regardless of the merits of a case.

“It’s a ground-breaking case that could result in a bank-breaking financial hit,” said Rafi Azim-Khan, head of data privacy at law firm Pillsbury.

($1 = 0.7201 pounds) (Reporting by Kirstin Ridley; editing by Barbara Lewis and David Evans)