HSBC has apologised after customers were unable to access online and mobile banking services.
The banking giant did not give a reason for the outage, which occurred on Friday morning, or specify the numbers of people affected.
A spokesman for HSBC said: "Our online and mobile banking services are now available. We are sorry for any inconvenience caused."
Several HSBC customers kicked up a fuss on social media, complaining of not being able to log in to their accounts and ripping into the lender over its poor customer service.
One Twitter user wrote: "@HSBC_UK Just replace your call centre with parrots that say 'use the web site' and put you on permanent hold if you already have. Cheap."
Another disputed the bank's claim that services were back to normal, saying: "UK online banking still isn't working despite your tweet saying it is!!!"
British banks are regularly hit with IT outages, and earlier this year customers with NatWest, RBS, Lloyds and Halifax also struggled with online glitches.
Some NatWest customers said cash appeared to have "disappeared into thin air" as attempts were made to transfer money in April.