The Royal Bank of Scotland and Natwest customers are unable to access online or phone banking services while others report that they cannot pay by card or via PayPal.
According to a number of customers that have spoken to IBTimes UK, as well as dozens of customers on Twitter, they are unable to access any online services, while a number say they are not even able to pay for goods by card after being declined since 1800 GMT.
Customers abroad have reported the same problems.
One person who contacted IBTimes UK said "My daughter is in Turku, Finland alone. Embarrassingly she has not been able to pay for dinner, or access any cash. Fortunately I have been able to buy a train ticket online for her to Helsinki tomorrow, but otherwise she has no access to cash. Very disappointed indeed. This isn't the first time."
Another customer said "currently in a restaurant for a meal with my mother and both of us have had our RBS debit cards refused by two different machines."
"Gone to three different cash points,can't withdraw cash either. A complete shambles."
"We are aware of some technical issues being experienced by customers and working hard to fix them. We apologise for the inconvenience caused," says a recorded voicemail when you call the customer service phone line, as well as the spokesperson that IBTimes UK contacted.
RBS received a taxpayer funded £45bn (€54bn, $73bn) bailout in 2008 which eventually led it to be 81% owned by the government.
While RBS said it is working on the problem, customers have emailed IBTimes UK to say that they are unable to pay for their bills online.
"I've tried to pay some bills this evening - to no avail. Worrying," said one customer to IBTimes UK.
History of Problems
RBS and one of its retail subsidiaries Natwest are no strangers to technical faults for its consumer banking services.
In August 2012, RBS revealed that it had put aside £125m to compensate thousands of customers affected by a two-week computer breakdown, which led to millions of customers being stranded without case and without being able to pay for outgoing bills.
In April this year, Britain's financial watchdog said it will investigate RBS over its 2012 computer failure that left millions of customers unable to access their accounts.
The Financial Conduct Authority launched an enforcement proceeding into the IT failures which occurred in June and July 2012.
"The FCA will reach its conclusions in due course and will decide whether or not enforcement action should follow that investigation," the statement said. RBS had around 17m customers at the time of the system failure but has never confirmed how many were affected by the fault. It set aside £125m in August of last year to compensate affected customers.
The now ousted RBS CEO Stephen Hester admitted the bank had "let down" customers because of the system-wide failure and apologized to customers and shareholders.
UPDATE (2145 GMT)
While there is no official update from RBS spokespeople, some customers are reporting to IBTimes UK that they are able to pay for goods via PayPal again.
However, only a number of others say they are able to use online banking again.
UPDATE (2213 GMT)
More RBS and Natwest report online banking services are working.