Lloyds Banking Group has apologised after customers were left unable to use their cards or withdraw cash for hours following an IT glitch.
Customers of Lloyds, TSB, Halifax and the Bank of Scotland - who are all owned the by the group - experienced problems yesterday afternoon.
Debit card transactions were disrupted for three hours and cash machines for four and a half hours before the difficulties were resolved.
A spokeswoman for the group said last night: "Although the majority of transactions were unaffected, we are very sorry for the inconvenience that this will have caused.
"At the same time, some customers encountered problems at approximately half of our 7,000 ATMs. This was resolved by 7.30pm, and all of our ATMs are now working."
Online and telephone banking were unaffected by these issues, and customers were still able to withdraw cash from other ATMs.
TSB chief executive Paul Pester said in a tweet that hundreds of people were queuing to talk to customer services about the issue.
"At one point we had 300 customers queuing to speak to the call centre - sorry if you couldn't get through," he said.
"Thanks to all TSB colleagues who worked so hard this afternoon to fix the IT issues. Sorry once again to all our customers affected."
He blamed the problem on a "server failing" in the UK and confirmed all brands under Lloyds Banking Group were affected because they share the same IT system.
Disgruntled customers took to social media to express their dissatisfaction.
Carl Bullivant tweeted: "Wife's card declined in Asda had to go get my card from home how embarrassing standing and waiting #poorbankingservice."
Essie Young wrote: "Didn't even want to be a @TSB customer when LTSB split! Couldn't buy my twins bday presents today with TSB card! #fuming #customerservice."
Another customer tweeted: "@TSB left me unable to pay for my shopping and no access to my money. TSB are a joke."ATMs are now working."