Many NatWest and RBS customers have been left short of cash after payments into their account simply 'went missing'.
The bank acknowledged that there was "a technical issue with payments crediting for some customers" and said it was investigating as a "matter of urgency".
The Daily Mail has claimed that as many as 600,000 payments disappeared overnight.
Some Customer payments are missing this morning – we are investigating this issue as a matter of urgency. 1/2— NatWest Help (@NatWest_Help) June 17, 2015
If you have been affected and need to access funds today, please contact us 03457 888444 or visit your branch 2/2— NatWest Help (@NatWest_Help) June 17, 2015
The bank says, although the issue has now been identified and fixed, customers may have to wait until Saturday for the payments to show up in their accounts.
Unsurprisingly, customers have been left unimpressed by the glitch, which has left some critically short of cash.
@Leedsmag84 took to Twitter to warn that he would be switching banks if his money did not arrive soon, while @Dawnykins80 claims she was missing payment on which she desperately relied.
The bank has insisted that "no customer will be left out of pocket or encounter any fees or charges as a result of this issue."
@NatWest_Help Hi Natwest, is there a problem? my Payment which was due today and which I desperately rely on isn't showing in my account :(— Dawn Mitchell (@Dawnykins80) June 17, 2015
Nicolas Frankcom, from uSwitch.com, says anyone affected needs to keep a close eye on outgoing payments.
"If you're a Natwest, RBS, Coutts or Ulster Bank customer and have a payment coming up, it's worth contacting the company or person you're paying so that they're aware of the issue.
"This is especially important with credit card, loan or mortgage repayments as you do not want to risk a 'black mark' going on your credit report."