According to reports, an IT issue at 14:00 BST on Saturday (August 18th) led to customers being unable to withdraw funds, pay for products by card or use the bankâs online services for a 20 minute period.
Many customers are reported to have been forced to leave purchases at shop tills and the bankâs call centre received numerous complaints.
A spokeswoman for the bank said: âWe became aware of the problem - which was resolved quickly - early on Saturday afternoon. We apologise to customers for any inconvenience."
She added that the bank is still investigating the reasons behind the glitch âas a matter of priorityâ.
It is not yet known exactly how many of Barclays customers were impacted by the issue.
The bank recently announced details of a contract with NCR Corp over the management and maintenance of its remote ATM system.
Under the terms of the deal, financial technology provider NCR will be responsible for running the 550 host operated and off site machines for the next two years.
By Jim Ottewill