Visa has said that a "service disruption" had hit its payment system, leaving some businesses unable to process purchases by its cardholders.
The extent and cause of the hours-long outage that began Friday afternoon was unclear, but customers across the continent filled social media with posts in which they vented frustration.
British lawmaker Angela Rayner tweeted that she left a petrol station without paying.
"First time I've ever left without paying for my fuel #visa fail," she wrote, adding: "Good job my local garage knows me."
Many businesses in Britain posted handmade "cash only" signs on their storefronts, while grocery shoppers reported long queues and chaos at supermarkets such as Sainsbury's, Tesco and Aldi.
"We are currently experiencing a service disruption which is preventing some Visa transactions in Europe from being processed," the US-based card giant said in a statement.
"We are investigating the cause and working as quickly as possible to resolve the situation. We will keep you updated."
Later Friday, Visa apologised for the outage and said it was "currently operating at close to normal levels."
"The issue was the result of a hardware failure," it said in a statement.
"We have no reason to believe this was associated with any unauthorised access or malicious event."
Barclays and the Bank of Ireland told customers that they were aware of the situation and encouraged people to make withdrawals at cash machines.
Santander UK said it was receiving an "extremely high volume of calls" to its customer service centre, while British lender HSBC said Visa was "working hard to resolve the issue as quickly as possible."
Visa rivals American Express and Mastercard were not affected.