Nationwide Building Society has apologised to customers after a technical hitch left some people temporarily locked out of internet banking and mobile apps.
The society said the IT problems started this morning and they were "intermittent", with some users who could not log on finding they were then able to do so a couple of minutes later.
Nationwide, which is Britain's biggest building society, said not all customers were affected by the problems, which its IT team was working to fix as soon as possible.
It said the latest issue is unrelated to a separate technical glitch which occurred on Wednesday and affected some customers.
A spokesman for Nationwide said the society apologised for the problems.