The Royal Bank of Scotland (RBS), which also owns NatWest, has apologised after its cashpoint, online and telephone banking systems crashed.
RBS cards are now working. Natwest customers, unable to get cash from ATMs, can use chip-and-pin machines.
A spokeswoman said: "We are very sorry, and we're working to sort it out."
'Very frustrating'
She added that until the problem was identified and fixed, customers could get cash from retail outlets which offered cashback.
Guy Swanwick, 45, from Liverpool, told the BBC News website he tried to access cash at 2300 on Friday 1 June near his home, but was unable to do so.
Mr Swanwick, who is disabled, said: "I tried 12 cashpoints without success.
"I ran into several other NatWest customers in the same position. It was very frustrating."
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Never liked NatWest - always thought their customer service sucked!!! Could be quite annoying not being able to get to your cash when you are out on a bender