TSB this morning took down its online banking systems with its boss issuing a fresh apology to customers and promised to compensate those affected.
The lender's mobile app and online banking was taken offline at around 10.30am.
Chief executive Paul Pester said:
Ive just resurfaced after 48 hours with my teams who have been working as hard and fast as they can to get our services back up and running. This isnt the level of service that we pride ourselves on providing, and isnt what our customers have come to expect from TSB, and for that Im truly sorry.
"Were still seeing issues with access to our digital services. One of the steps we need to take to resolve this is to take our mobile app and online banking down for a few hours. Weve taken this offline at around 10.30 this morning and we hope to be back up later this afternoon. Well let your customers know as soon as its available again.
"Of course, customers can rest assured that no one will be left out of pocket as a result of these service issues."
TSB's update comes as the chair of an influential parliamentary committee demanded answers on the online outage.
Customers had been warned that TSB was planning an upgrade to its systems, with that taking place between 4pm Friday 20 April and 6pm Sunday 22 April.
When TSB split from Lloyds, it had continued to use a banking platform from its former owner while developing its own one. The process of moving across to that was over the weekend, and that disruption was planned, but customers have been reporting troubles long after the 6pm deadline.
But the planned upgrade blocked some people from accounts for more than the two anticipated days, and gave some customers access to others' accounts – including allowing them to transfer money
Both the Financial Conduct Authority (FCA) and the Information Commissioner's Office (ICO) have made contact with TSB about the problems
A spokesperson for the FCA said the City watchdog is "aware of the issue and liaising with the firm".