Santander’s services have gone down in a major outage.
Customers reported being unable to get onto online banking, make transactions and other issues.
It comes after a run of outages across the high street, which have taken apps of many major banks briefly offline.
On Twitter, Santander said it was aware of the issue and working to fix it.
“We’re aware that customers are currently unable to access some of our services,” it said. “We’re very sorry for the inconvenience this is causing, and we are working hard to fix the problem as soon as possible.”
Data published by the Treasury Committee on Thursday revealed there have been more than 33 days' worth of unplanned tech and system outages in the last two years for nine of the UK's biggest banks and building societies.
Experts have previously said the banking sector and regulators are struggling to keep up with modern technology and embedding it in their large, complicated and often dated technology systems.
According to the Santander website, the bank is having issues with its mobile banking, telephone banking, technical problems within its branch network and card payments.
However, it said cash machines and online banking were available as normal.
According to service status website Downdetector, Santander customers began reporting issues with the firm's services at around 12pm on Thursday, with more than half of those reports flagging issues with payments.
On social media, users reported a range of issues, from being unable to log in to their account or the firm's app, to making payments or transferring funds.
In a message on the Santander website, the bank said: "We are currently facing intermittent issues making payments that we are working hard to resolve.
"If you face issues please try again, and in case of continuing failures please use Online Banking in the meantime."
It also had similar messages for its telephone banking, branches and card payments services, and said it would provide further updates to customers via its website and social media pages.
Additional reporting by agencies
Santander users hit by outage affecting banking app and other services
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