Millions of Mastercard users could get up to £70 each after a court ruled that historic fees charged by the provider to be unfair.
The decision comes after a long-running legal case going back a decade, brought forward by a former financial ombudsman.
Walter Merricks argued that shoppers were charged higher prices after fees were wrongly levied on transactions made over a 15-year period between 1992 and 2008.
Mastercard has been approached for comment.
Mr Merricks said that, despite retailers paying the fees, shoppers had lost out as retailers passed on these costs in the form of higher prices.
The former financial ombudsman launched his claim after the European Commission ruled in 2007 that Mastercard’s “multilateral interchange fees” charged to businesses had infringed competition law since the year 1992.
He alleged that 46 million shoppers in Britain were overcharged.
The fees were paid by retailers accepting Mastercard payments, rather than by consumers themselves.
