A leading mortgage lender is set to repay an estimated €30,000 to borrowers after discovering it overcharged them on home loan arrangement fees.

IIB Home Loans, a division of Belgian-owned bank, IIB, has written to more than 300 borrowers to inform them of the mistake.

It has pledged to repay the money with interest.

The total amount involved is said to be just under €30,000. On average, it owes each customer €80, but a small number of borrowers are owed in excess of €1,000.

IIB Home Loans yesterday blamed human error.

A spokesman said that it had mainly occurred in the late 1990s, and that the number of mistakes had decreased as it upgraded its computer systems over the last five years.

The bank also discovered that it had undercharged a number of customers.

It said that it would not be seeking to recover this money.

It has informed the Irish Financial Services Regulatory Authority (IFSRA) about both errors and the steps it is taking to compensate customers.

This is the latest in a line of Irish financial institutions that have admitted overcharging their customers.

IFSRA recently issued a report stating that AIB deliberately sought to hide the fact that it overcharged foreign exchange customers by €34.2 million.

Since then, Irish Life & Permanent has said that it intended to repay €400 to 1,500 customers who paid more mortgage interest than they should have.

IIB discovered its mistake in the course of an internal review of charges that it has been working on since the summer.

IFSRA told all Irish financial institutions to carry out these reviews after the AIB overcharging scandal was revealed earlier this year.

IIB Home Loans has around 12 per cent of the Republic's lucrative mortgage market, making it one of the bigger players in this sector.

Mid-way through this year, it told The Irish Times that the total value of its book was €4.4 billion and that it had 40,000 borrowers.