MasterCard will be subject to a class action suit over anti-competitive and deceptive fees.

This may not seem to be a big deal to Americans, but this is a first in British jurisprudence, and marks a major change in consumer law:

The UK Supreme Court on Friday allowed a 14 billion pound ($18.5 billion) class action to proceed against Mastercard for allegedly overcharging more than 46 million people in Britain over a 15-year period in a landmark judgment.

The complex case, brought after Mastercard lost an appeal against a 2007 European Commission ruling that its fees were anti-competitive, could entitle adults in Britain to 300 pounds each if it is successful.

The court dismissed a Mastercard appeal, setting the scene for Britain’s first mass consumer claim brought under a new legal regime and establishing a standard for a string of other, stalled class actions.

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The case will now be sent back to the Competition Appeal Tribunal (CAT), nominated in 2015 to oversees Britain’s fledgling, U.S.-style “opt-out” collective class actions for breaches of UK or European Union competition law.

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The case centres on so-called interchange fees which credit and debit card companies say they levy on merchants’ banks to cover the costs of card services, security and innovation.

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Anthony Maton, the global vice-chair of law firm Hausfeld, which is advising on other class actions, said: “This is a revolution in English law.”

This is indeed a big move, and a welcome one.