Some 1,200 bank branches of NatWest, the Royal Bank of Scotland (RBS) and Ulster Bank are opening on Sunday for the first time ever, after a computer glitch left their accounts frozen for three days running.

The problem reportedly has affected customers up to 12 million of NatWest, RBS and Ulster, which are part of the taxpayer-owned RBS Group.

The computer glitch has made the customers unable to pay bills or move money, and savers' accounts frozen.

Stephen Hester, chief executive of RBS Group, issued a public apology on the website for the technical hitch and admitted the problems of the past few days have caused disruption and inconvenience for our customers as well as for many customers of other banks.

Hester said, "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."

Although the technical error is fixed, the bank branches have to stay open on Sunday to clear the backlog of transactions for the customers, who have unpaid salaries and rent payments not being processed.