A £14bn group damages claim against Mastercard reached the Supreme Court by video last week. In the first action to be brought under the collective action regime introduced by the Consumer Rights Act 2015, the court was urged to allow a claim on behalf of 46 million consumers to proceed to the next stage of litigation.

The highest court is being asked to decide whether to uphold the Court of Appeal’s decision to remit an application for a collective proceedings order to the Competition Appeal Tribunal, which refused an application in 2017.

The proceedings hinge on fees imposed by Mastercard on businesses between 1992 and 2008. It is alleged that all customers who bought from shops that accepted Mastercards – regardless of whether they used a Mastercard themselves – suffered loss as a result of higher retail prices. The opt-out claim is brought by former financial services ombudsman Walter Merricks CBE. Mastercard denies liability.

For Merricks, Paul Harris QC said collective proceedings are the only way to ensure access to justice for consumers: ‘If we do not proceed [with the class action] then we will not proceed at all. It is no accident that there are no individual claims.’

However, Mark Hoskins QC, for Mastercard, said that claims are not suited to an aggregate award of damages and stressed the difficulties of calculating alleged loss.

‘In 1992, the start of the claim period, half a million retailers in the UK accepted payment by Mastercard cards,’ he told the court. That had risen to some 800,000 merchants by 2008. Experts accepted that there was likely to be ‘significant variation in the extent merchants in different sectors of the economy… passed on any overcharge to their customers by way of higher retail prices’, Hoskins said.

Levels of overcharge could vary within each sector of the economy, as well as geographically, Hoskins added, stressing the dearth of relevant data. ‘What the… application would require is the tribunal to conduct a full trial across all the sectors of the UK economy.’

In response, Harris said more data would emerge during the disclosure phase of proceedings and the current methodology for working out ‘downstream pass-on’ was ‘credible and plausible’. He added: ‘There isn’t an unlimited budget at the collective proceedings order stage. This is an expensive business.’ The claim is being fully financed by Innsworth Litigation Funding.