An urgent investigation has been launched into payment failures at Sainsbury's and Greggs stores

Sainsbury's had problems processing payments and deliveries on Saturday. Photo: Dinendra Haria/LNP

Standout line IT failures that have led to sales at Greggs, McDonald's, Tesco and Sainsbury's stores in recent days are being reviewed by the payments watchdog

The Payment Systems Regulator (PSR) said it is reviewing the outages over the past week to see whether further action is needed amid potential concerns about the sustainability of payments infrastructure.

It is liaising with companies and liaising with the Bank of England regarding the unusual string of failures.

The study comes as the decline in cash is making shoppers increasingly reliant on digital payment systems.

Cash has fallen from 54% of all payments in 2012 to 14% in 2022, according to UK Finance, and a growing number of retailers are refusing to accept cash.

Greggs on Wednesday became the fourth major retailer in five days to have problems accepting payments.

An IT glitch stopped hundreds of checkouts and forced some stores to close. The bakery chain blamed a «technical issue,» prompting a flood of complaints on social media, and then said it had fixed the problem.

Greggs apologized to customers after the glitch forced about a third of its stores to close on Wednesday. Photo: Phil Barnett/PA

Last Friday, McDonald's was forced to close several restaurants due to a payment glitch that it said was «caused by a third-party vendor during a configuration change.»

Sainsbury's and Tesco are having problems processing and processing payments. deliveries on Saturday.

«PSR is aware of recent payment issues and is assessing their nature to determine whether any further action is necessary,» the spokesperson said.

PSR is monitoring major UK payment processors such as Mastercard, Visa and the Faster Payments Scheme rather than individual retailers. If it identifies a problem with the sustainability of the payment infrastructure, it may refer the issue to the Bank of England.

Payments and security experts have found no clear link between the problems on the four chains, although the number of outages in a short period of time has raised suspicions that a software update from a common provider led to the bugs.

One payments consultant said, that the leading theory in the industry is that this may be due to third-party «electronic point of sale» (EPOS) software that links payments to inventory management and order recording.

EPOS systems often process barcode scanning. This may explain why Tesco and Sainsbury's struggled to deliver online on Saturday as staff were unable to scan items as they went into delivery baskets.

Retailers typically do not disclose details of their payment processors, in part because it could make them more vulnerable to hackers.

Security experts said the problems do not appear to be the result of cyberattacks on the companies.

“It appears a mistake, but a lesson learned in terms of how vulnerable we are,” said Professor Alan Woodward, a cyber security expert at the University of Surrey. «This potentially shows what would happen if an attacker penetrated the supply chain.»

Greggs apologized to customers on Wednesday after a glitch left about a third of stores unable to access payments.

Sainsbury's promised to pay compensation to affected customers.