Ulster Bank has been forced to admit that it has undercharged more than 1,000 mortgage customers around €30,000 each.

It was the latest scandal to hit the bank which experienced an IT meltdown last summer which left hundreds of thousands of people without access to their accounts.

This latest error involves at least 1,300 mortgage customers from whom around €40 million was not collected.

They have been told they will have to pay the money back.

In a statement to the Irish Independent, the bank is quoted as saying "Ulster Bank self-identified an under-payment error affecting some mortgage accounts".

"All impacted customers are being contacted, given time to make repayments and (can) choose from a number of repayment options" it added.

It is unclear whether the bank will be charging interest on the repayments.

'Questions need to be answered'

Labour Senator Lorraine Higgins says questions need to be answered.

"I am most concerned but not surprised by the news that Ulster Bank, is yet again causing undue worry and concern to their customers, this time through their own mismanagement of mortgage accounts" she said.

"It is worrying that the office of the Financial Services Ombudsman said this recent problem had not been brought to his attention, and that all those mortgage customers affected have yet to be notified".

"The question needs to be put to Ulster Bank as to how such an error could occur in the first instance and persist without detection for such a long period of time" she added.

CEO of the Consumers Association of Ireland is Dermot Jewell.

He says the whole issue is highly unacceptable for customers.