A £14bn class action against Mastercard for allegedly overcharging 46 million British consumers during a 15-year period has been given the green light to proceed. Almost every adult in the UK – even if they never had a Mastercard – could receive a payout of up to £300 from the credit card company after a supreme court ruling paved the way for the class action lawsuit. The legal action taken by the former financial ombudsman Walter Merricks claims that 46 million UK consumers paid higher prices in shops over a 16-year period because of allegedly excessive transaction fees charged by the company. The judgment upholds a decision by the court of appeal last year and sets the scene for a mass consumer claim. The supreme court dismissed an appeal by Mastercard in the latest chapter of the vast, complex case, which was brought after the company lost a drawn-out appeal against a 2007 European commission ruling that its fees were anti-competitive. “Mastercard has been a sustained competition law breaker, imposing excessive card transaction charges over a prolonged period in a way it must have known would impose an invisible tax on UK consumers,” Merricks said, adding that the prices of “everything we all bought from 1992 to 2008 were higher than they should have been”. Merricks claims the maximum payout would be about £300 for anyone who can prove they were in the UK in the 16 years between 1992 and 2008. Some 46 million adults could qualify and they need never have held a Mastercard. The credit card company said it fundamentally disagreed with a claim that it said was being driven by “hit and hope” US lawyers. “Mastercard will be asking the Competition Appeal Tribunal (which will oversee the case) to avert the serious risk of the new collective action regime going down the wrong path with a case which is fundamentally flawed,” it said in a statement. The ruling was welcomed by consumer groups, with Which? calling it an “important win”. Its director of policy and advocacy, Rocio Concha, said: “Which? has campaigned long and hard for an effective collective redress scheme and the supreme court’s ruling will increase access to justice for consumers and set the standard for collective claims of this nature to proceed to trial. “From today, the route to collective redress will be fairer, simpler and more attainable, and many cases that are currently on hold will be able to proceed to trial, ensuring victims of anti-competitive behaviour can get the justice they deserve.” Legal commentators have suggested that the decision will have ripple effects and there will be an increase in the number of class actions filed in the future. Kenny Henderson from the law firm CMS said: “The bigger concern for business more generally is that the supreme court ruling will encourage claimant law firms to file more class actions against other large companies. We could see many more large claims being filed – and a shift towards the class action culture that we associate with the US.”