AT LEAST 13,000 Ulster Bank and First Active customers have been told their banks under-deducted Deposit Interest Retention Tax (Dirt) on their savings accounts. The two banks have written to affected customers in the past week about the miscalculation of Dirt. A spokeswoman for Ulster Bank said letters had been sent to 6,500 customers of its subsidiary, First Active.

She declined to say how many Ulster Bank customers were affected but indicated it was greater than the number of First Active cases, but small in the context of the two banks’ 1.9 million customer base.

The bank says the miscalculation occurred as a result of a systems error and the average amounts involved for each customer are small – just €1 in the case of First Active.

The mistake was spotted in an internal review which showed that the wrong rate of Dirt was applied to the bonus element of some deposit accounts.

Both institutions continued to deduct 20 per cent Dirt from bonuses after January 1st this year, when the Government imposed a new rate of 23 per cent.

In each case, the incorrect amount credited to a customer’s account has been reversed and the correct deduction made. No action is required on the part of customers.

Both First Active and Ulster Bank have apologised to customers and assured them that the problem would not arise again.