Customers belonging to NatWest, the Royal Bank of Scotland and UlsterBank have been warned that problems affecting online banking services may persist for a number of weeks.
Here's the latest on what you need to know about the disruption.
Martin Rickett, PA Wire
Why have customers been experiencing difficulties?
A computer problem began late on Tuesday 19 June following an attempt to install an update to payment processing software belonging to the Royal Bank of Scotland (RBS).
Customers discovered they could not access their online accounts, that they were missing salary and wage payments, or their rent or mortgage repayments had not been processed.
The issues also affected customers belonging to NatWest and Ulster Bank, which are owned by RBS.
When will the problems be fixed?
The computer issue was resolved over the weekend if 23 and 24 June, but the company is continuing to run tests to check the online system.
The Financial Ombudsman Service has warned that it could be several weeks before the consequences of the technical malfunction have been sorted out.
What sort of problems have been caused by the computer failure?
A defendant in a court case had to spend the weekend in prison because the disruption prevented his bail money being transferred.
In another case, at Westminster Magistrates' Court in London, a judge is believed to have used his discretion to grant a defendant bail even though the same problem had occurred.
More general problems have included customers being unable to view an up-to-date balance of their account, payments such as direct debits for bills not being made and wages not been received.
What has RBS done to deal with the problems?
- Extended the opening hours of thousands of branches to 8am - 6pm for the rest of this week
- Doubled the number of call centre staff to deal with problems and complaints
- Promised to reimburse customers for the cost of calling its 0845 helpline number
- Vowed to automatically waive any overdraft fees or charges on current accounts; this will be processed over the next few days
- Pledged to work directly with credit agencies to ensure nobody has their credit score affected
- Said that customers stranded because of the computer problem will not be left out of pocket
How will RBS ensure that people will be properly compensated?
Susan Allen, the director of customer services at RBS, has said: "Customers have our commitment that they will not be out of pocket from this issue. We will publish further details on how we will ensure this later in the week."
Has RBS issued a formal apology?
Yes. A statement from RBS chief executive Stephen Hester was posted on the RBS website on 25 June. Mr Hester says:
"I am very sorry for the difficulties people are experiencing. Our customers rely on us day in and day out to get things right, and on this occasion we have let them down. This should not have happened.
"Right now my top priority, and the priority of the entire RBS Group, is to fix these problems and put things right for our customers.
"This is taking time, but I want to reassure people that we are working around the clock to resolve these problems as quickly as we are able."
What political reaction has there been?
Shadow chief secretary to the Treasury, Rachel Reeves, has told Sky News it was "absolutely imperative that RBS gets a grip on this situation".
The Liberal Democrat peer Lord Oakeshott has said: " Enough is enough. RBS have failed the nation for years on lending to small business - now for millions of hard pressed people in hard times, blocked money pipes are as awful as blocked water pipes."
Are you continuing to experience problems with your RBS, NatWest or Ulster Bank account? Leave a comment below.