TSB problems: computer fiasco enters fifth day as customers still unable to use online banking despite services being 'back up and running'

TSB's computer "meltdown" has entered a fifth day with thousands of customers still locked out of accounts and unable to make payments.

The bank today said its mobile banking app and online services are "up and running" but frustrated customers are still reporting receiving an error message when trying to log on.

The number of customers able to log in at once has been limited as the bank expects a surge in people attempting to get online.

Chief executive Paul Pester said on Tuesday he was "deeply sorry" for the problems, which left some customers able to see other people's accounts, as data and banking watchdogs confirmed they were looking into the situation.

It follows a shift to a new IT system after TSB's split from the Lloyds Banking Group.

The bank had told its account holders that some of its services, including online banking, making payments or transferring money, would not be possible over the weekend.

The upgrade window was scheduled between Friday at 4pm and Sunday at 6pm.

But thousands complained of problems with mobile and online accounts three days after the upgrade was supposed to have been completed.

One customer said they had "access" to other customers' accounts totalling more than £20,000 and another reportedly discovered they had been credited with £13,000 after logging back in.

The bank's boss announced on Twitter on Wednesday morning that the services had been restored and thanked customers for their "patience and bearing with us".

But a number of frustrated customers on social media said they were still unable to access their money.

Using the hashtag #TSBFail many said they encountered an error message when trying to log in.

The Information Commissioner's Office, which monitors data and privacy, said: "We are aware of a potential data breach in relation to TSB and are making inquiries."

Banking regulator the Financial Conduct Authority said: "We are aware of the issue and are liaising with the firm."

MPs demanded answers from the bank about the IT meltdown.

Treasury Select Committee chairwoman Nicky Morgan wrote to Mr Pester asking for details of the problems and the bank's response.

She said: "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."

TSB said a "tiny fraction" of customers saw accounts belonging to other customers and the issue was resolved in about 20 minutes.

TSB's social media team faced a stream of complaints from customers, including several who said they could see other people's accounts after logging back in on Sunday evening.

Craig Malcom tweeted: "@TSB I currently have access to £20k+ of other peoples money.

"This is a MASSIVE breach of data protection! If i have access to their account they could have to mine as well!"

Another Twitter user called Bex said: "@TSB so go to my app and have someone else's accounts there!!!! Serious dpa (Data Protection Act) breach! Want to speak to someone now and a half an hour wait!! What would the FCA (Financial Conduct Authority) say about this!!! Might just inform them a bank is giving away other people's account numbers".

Laim McKenzie, from Paisley in Scotland, told the BBC he had been unexpectedly credited with thousands of pounds after logging back in after 6pm on Sunday.

"My balance, because of my overdraft, is in minus, but my balance was showing at £13,000," he said.