After more than a week of problems, half of TSB's online banking customers are still locked out of their accounts, and it is unclear exactly when the disruption will be resolved.
TSB's chief executive Paul Pester said last week that the bank was "on its knees" and is unsure what has caused the IT meltdown. A team of experts from technology giant IBM has been drafted in to solve the issue.
Customers have faced a week with no, or intermittent, access to their accounts, following a migration of some of the bank's services to a new platform, which involved moving 1.3 billion customer records.
- Q&A on your rights in the TSB fiasco below
This was scheduled to be complete by 6pm on Sunday. However, on Sunday evening, customers reported that they were able to view other people's accounts when they logged in to their own, including account numbers and sort codes.
TSB took its systems offline to fix the issue, but since it put them back online at 2am on Monday, customers have struggled to access their accounts, and have reported a range of other issues.
TSB chief executive Paul Pester said in a statement on Tuesday that the bank's mobile application and online banking services were being taken offline once again, but that he expected everything to be up and running again on Tuesday afternoon.
However, the services were still down late into the evening, with TSB saying it was still working to resolve the issues. On Wednesday morning, TSB said both online and mobile banking were back up and running, but that it was limiting the number of people who can log in at any one time.
On Thursday, TSB took its services offline once more, and later announced on Twitter that its online and mobile banking services were "back up and running".
The bank then once again took its internet banking services down temporarily on Sunday. After putting them back online, the company said via Twitter that "customers may still have difficulties accessing and using these services".
Last night a spokesman said: “Internet banking is currently operating at around 50 percent of capacity,” a bank spokeswomen said: "For every ten customers who try to access our internet banking, five will be able to access this service.”
Could anyone see my account?
TSB said that for 20 minutes on Sunday evening, linked (or nominee) accounts, where someone other than the main account holder is given restricted access to the account, were accessible to those additional people via online banking.
Around 2pc of TSB’s five and a half million customers, or 110,000 people, use such an account. TSB says the number who actually did log in and see such information was 402, and that all the evidence it has seen so far points to the issue being limited to these accounts.
However, a number of people claiming to be TSB customers have told Telegraph Money that they were able to view accounts that they had no affiliation to.
Niall McDonnell, 28, told Telegraph Money that he was able to see a business account on his profile when he logged in, which contained over £2.8m. He said that he sent a screenshot to the City watchdog and the Information Commissioner's Office.
Jenny Bateman, 26, said she could see account numbers and sort codes of accounts that weren't hers, and that she is not involved in any linked accounts.
Ashley Tait, 25, said that her father was able to see her account details and balances when he logged in to his own account.
.@TSB so go to my app and have someone else’s accounts there!!!! Serious dpa breach! Want to speak to someone now and a half an hour wait!! What would the FCA say about this!!! Might just inform them a bank is giving away other people’s account numbers— bex (@Bec_701) April 22, 2018
Have there been other problems?
Customers have used social media to report a host of other problems, including lengthy waiting times to get through to customer services, incorrect balances, and the disappearance of accounts.
On its website, TSB has now admitted that customers are facing many of these problems, including errors when making payments, the disappearance of mortgage accounts when viewed online, and errors when resetting login details.
Up until now, TSB had refused to acknowledge wider problems, and questioned their legitimacy.
Darren McCormick, 32, said that his account balance was incorrectly reduced to £0, and his card stopped working when he tried to pay for petrol.
He claimed that a TSB customer service adviser instructed him to write a letter to the service station explaining that he would pay them back.
"I have been with the bank for 12 years and I certainly won't be a customer for a 13th. I have now lost all trust," he said.
Others have been left unable to make bill payments due to the disruption.
A number of customers have said that they will be closing down their accounts with the bank as a result.
TSB has apologised "unreservedly" to customers.
Why has this happened?
Last weekend, there was a planned migration of customer data from a banking platform rented from Lloyds Banking Group to TSB's own platform. A total of 1.3 billion customer records had to be moved.
TSB switched off a number of services over the weekend while it made the switch. When it brought its system back online on Sunday evening, customers began noticing that they were able to see other people's accounts when they logged in.
A spokesman for TSB said that only "nominee" account holders were affected. These are accounts that can be accessed by a designated person other than the account holder, but supposedly only in branch or via the phone.
TSB's spokesman said: "When we brought our systems back online after the migration, we noticed that nominees were able to access those accounts online. They would have been able to carry out a transaction."
This lasted for 20 minutes, until TSB took its system down again until 2am on Monday morning.
However, some customers have reported being able to see accounts of people or companies they have no affiliation with.
On Monday, many customers were unable to access their accounts at all, which TSB put down to "very high volumes of people" attempting to use the service.
Since then, problems have continued, with TSB taking down its services at various points. It has now had to draft in external help to solve the problems, after admitting it did not know what had happened.
How many people are affected?
Around 2pc of TSB’s five and a half million customers, or 110,000 people, use a linked account. TSB says the number who actually did log in and see account information that was not their own was 402, and that all the evidence it has seen so far points to the issue being limited to these accounts.
The total number who have not been able to access their own accounts due to the disruptions since Monday is unknown, although the bank has just under two million online banking customers.
What are my rights?
In the event your bank suffers technical problems that prevent access to your accounts, you can claim compensation for any losses incurred.
That includes any charges for late payment, extra costs incurred such as credit card interest, and any knock-on costs from not being able to make a payment.
There is also scope to claim for non-financial harm, such as the stress caused.
You can ask the bank to have your credit file corrected if not being able to access your account leads to negative consequences for your credit score, such as missing a credit card payment.
Mr Pester has assured customers that they will not be left out of pocket.
Of course, customers can rest assured that no one will be left out of pocket as a result of these service issues.— Paul Pester (@PaulPester) April 24, 2018
How do I claim?
To claim, first gather any evidence you might need, such as receipts, emails, invoices, or a copy of your credit file. You need to be able to prove the loss.
Then get in touch with your bank via the complaints department, detailing what happened and what you want them to cover.
If you feel that the bank doesn't handle your case satisfactorily, you can complain to the Financial Ombudsman. It will adjudicate on the dispute, and can order a bank to pay compensation.
When will it be resolved?
Customers are still reporting difficulties in accessing their accounts.
It remains unclear when TSB will be able to fully resolve the issues faced by customers, and they have already extended to the last day of the month, when many people are paid.
Mr Pester said that TSB is working "as hard and fast as they can" to resolve the problems.