The former financial services ombudsman behind a £14 billion lawsuit against Mastercard on behalf of 46 million consumers hopes to appeal its dismissal.

Walter Merricks has asked for permission to appeal after the Competition Appeal Tribunal (CAT) turned down the class action against the card firm last month.

Merricks claims Mastercard broke competition law by charging excessive so-called 'interchange fees' – the fees a retailer pays to your credit or debit card company when you use your card – between 1992 and 2007.

Retailers would have then passed on these charges to consumers in the form of higher prices, Merricks says, though Mastercard "strongly" opposes the claim.

The claim was brought on behalf of ALL affected UK shoppers – unless they chose to opt out of it – and would likely have affected anyone living in the UK, who was of working age between 1992 and 2008, regardless of whether they had a Mastercard.

However, the CAT queried a lack of evidence and how the loss – estimated to be in the £100s for each of the 46 million – could be established.

If Merricks' appeal application is successful, his team says it's unclear whether they would be able to go directly to the Court of Appeal or whether they need to go to the Administrative Court for a judicial review.

A Mastercard spokesman said: "We believe that any appeal or review by Walter Merricks is without merit and that the Competition Appeal Tribunal’s judgment to refuse certification for the proposed collective action was the correct decision.  Mastercard maintains that this claim is completely unsuitable to be brought under the collective actions regime."