TSB's mobile app and online banking have returned to service after being disabled thanks to a botched IT upgrade and apparent data breach.
The meltdown had left the lender, which has five million customers, and its chief executive Paul Pester, under intense scrutiny after days of disruption which has left account holders in the dark over their finances.
TSB's digital banking services were taken offline for more than a day from 10.30am on Tuesday - nearly five days after an initial planned shutdown - only being brought back online in the early hours of Wednesday morning.
"Our mobile banking app and online banking are now up and running," Mr Pester tweeted at around 3.40am. "Thank you for your patience and for bearing with us."
Appearing on Sky (Frankfurt: 893517 - news) 's Ian King Live on Tuesday, Mr Pester said he apologised "profusely" to those affected but declined the opportunity, when asked, to offer to give up his bonus, saying that was a matter for the bank's remuneration committee.
He also insisted that "for the vast majority of our customers things are running very smoothly".
The bank had switched to new servers over the weekend, preventing its 1.9 million digital customers accessing their accounts from Friday afternoon.
However, it quickly became clear on Sunday evening that all had not gone as planned as scores of account holders turned to social media to complain - with some indicating they could even see other people's account details .
TSB acknowledged that 402 customers were able to view "some data that we would not normally show them online" for a period of 20 minutes on Sunday evening.
The bank said each person had "connected accounts" with the bank - typically created between family members and insisted their data was safe.
This issue resulted in services being shut down again for several hours on Sunday evening until 2am, but after they were turned on again, users experienced further problems when going online and there was a renewed shutdown on Tuesday.
The login and data protection problems have attracted interest from regulators and stinging criticism from the chair of an influential committee of MPs (BSE: MPSLTD.BO - news) at a time when the industry is facing a backlash over branch closures and a shift towards mobile banking.
TSB had previously blamed the continuing disruption on high volumes of customers trying to access the new systems.
The old servers it replaced dated back to TSB's ownership within Lloyds.
Mr Pester told his Twitter (Frankfurt: A1W6XZ - news) followers he was "deeply sorry" for the problems - seeking to explain his public silence on the issue to date by saying he had "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."
He added: "We're 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."
Customers continued to vent their frustration on Tuesday to complain about a lack of information.
Sky News has asked the bank to check whether it had contacted them by email since the login problems began.
TSB, which has five million customers in total, has pledged that no one will be left out of pocket, but that was of little comfort to many.
One customer called Lauren tweeted: "@TSB Day 5 of your systems being down/incorrect. Can't get through to anyone on the phone. This is absolutely ridiculous the minute I get through to someone I'll be closing my account!!"
Another wrote: "@TSB I need help. Please. My wages went in on Friday and I need to pay rent and other DD. My wages are not showing and I cannot login. I may go overdrawn I don't know what to do. I tried calling was on the phone 45mins and then got cut off. Please help I'm actually in tears."
The Financial Conduct Authority and Information Commissioner's Office are in contact with the bank, with investigations widely expected to follow the debacle.
It later emerged that the Treasury Committee of MPs, which has previously demanded better standards of banks following similar IT glitches, had written to Mr Pester to seek answers.
Nicky Morgan MP, who chairs the committee, said: "The reports of unauthorised transactions, access to other customers' accounts, and failures of in-branch services have all the hallmarks of an IT meltdown.
"This is yet another addition to the litany of failures of banking IT systems. Potentially millions of customers could be affected by uncertainty and disruption.
"It simply isn't good enough to expose customers to IT failures, including delays in paying bills and an inability to access their own money.
"Warm words and platitudes will not suffice. TSB customers deserve to know what has happened, when normal services will resume, and how they can expect to be compensated.
"I will be writing to the FCA in due course for their assessment," she added.