Co-op, Morrisons, and their payments processing provider ACI say they are working "as quickly as possible" to fix a problem affecting card payments in stores.

Long queues were seen outside some of the Co-op's convenience stores from Sunday amid the snow, and customers were encouraged to pay using cash.

Customers have taken to social media to complain about the situation.

One MP said the problem exposed the risks of letting cash use "wither".

ACI, which provides real-time payments processing for the retailers, said: "The current IT issues affect card payments at Co-op and Morrisons and we are working closely with the IT teams at both partners to resolve the problem as quickly as possible. We apologise to shoppers for any inconvenience caused."

The issue comes as contactless payments have taken off in the UK during the pandemic, with fewer consumers using cash to pay for groceries.

"We've experienced some technical difficulties with our card payments and are working hard to resolve this as quickly as possible," said a Morrisons spokeswoman. "We are sorry for any inconvenience this may have caused."

.@Morrisons staff saying it’s a National outage of their card payment systems. Absolute nightmare for the staff if true. https://t.co/SCEGLufxza

— Jen Bartram (@JenBartram) January 24, 2021

A Co-op spokesman told the BBC: "Our payment processing provider is working to correct an intermittent issue which has prevented a very small number of customer transactions from being processed.

"We would like to apologise for any inconvenience caused."

The BBC witnessed the card processing issue affecting some of The Co-op's stores meant that self-service checkouts had to be closed, requiring customers to queue to be served at tills manned by staff.

Iep
Mu local Co-op too.
Staff said it's been a problem all day.
Customers had to dash over to use the in-store cash machine then pay in cash. Long queues!!
Strangely, after my Barclays Debit Card was "declined" I tried my Smile Card and that worked first time!

— David of Nottingham (@DavidofNotting1) January 25, 2021

At some stores, customers queuing outside were warned on Monday evening that transactions had to be "cash-only" due to the ongoing issue.

Some customers said they had to use the convenience store's cash machine to withdraw money to pay for purchases.

However in other stores, the problem was intermittent, impacting some payment card brands, but not others.

Shadow economic secretary to the Treasury Pat McFadden said: "This shows the dangers of letting the cash network just wither away as use declines.

"The government promised legislation to secure nationwide access to cash a year ago. It hasn't been brought forward."