The Royal Bank of Scotland (RBS) costumers weren’t able to use their credit and debit cards due to a technology breakdown during the busiest online shopping day in a year.
The glitch has also affected the banks' websites and smartphone apps. RBS apologised to its clients, promising to cover their expenses caused by the failure, but has not specified the reason behind the problem.
"We are very sorry for the system issues that affected our customers this evening," said an RBS Group spokeswoman on Tuesday morning and reassured things were slowly getting back to normal.
"Our customers are reporting that services are coming back on line. We will confirm when all systems have returned to normal service. If customers have been left out of pocket as a result of these system problems, we will put this right," she said, advising the costumers to contact RBS call centres in case they are unable to resolve the situation.
First problems were reported at around 6:30pm on Monday when many costumers were left standing at the checkout in supermarkets with their trolleys full but unable to pay.
Many of those affected took social media by storm, complaining on Twitter about the embarrassment of not being able to pay for things like petrol or basic food. Apart from the RBS, the glitch affected also customers of Ulster Bank and Natwest – both belonging to the RBS group.
"Thanks #natwest for leaving me with an unpleasant petrol attendant when my business and personal card were rejected for fuel," Durham woman Nickie Gott tweeted.
Another affected customer complied on Twiiter: "Natwest is down. Just looked like a broke alcoholic attempting to buy booze, but apparently it is not my fault. Thanks Natwest."
The meltdown came amid a day dubbed Cyber Monday, when on-line retailers were experiencing the highest amount of transactions at the start of the pre-Christmas shopping season.
RBS Group, 82 per cent owned by the UK government, faced a probe by the Financial Conduct Authority in April when technology failure left customers unable to avail the bank's card and online services.
A software upgrade gone wrong also led to similar problems for RBS' customers in June 2012.