The Anglo Irish Bank, under former boss Sean Fitzpatrick and his management team, overcharged its customers by as much as $130 million on loans taken out between 1998 and 2004, the bank’s chief executive Mike Aynsley told the Irish Independent.

The overcharge will now be paid back, with interest, by taxpayers.

An investigation is ongoing, but Aynsley said the repayment figure should be somewhere between $38m and $64m.

"Bear in mind when this happened, this was pre-2004. So this is a long time ago, so it's going to take us a little while to get to the bottom of the full scale, if there is a full scale. We don't think that this is a very widely spread thing. There might have been a few small pockets of it over time and then it sort of stopped so we suspect it was driven by some kind of process errors," said Aynsley.

He said he didn’t know yet if there was any evidence of deliberate overcharging by the old management.

"There is a statute of limitations and, theoretically, we're probably not compelled to go back beyond a six-year period, but because we believe there are important ethical issues around this for us and our customers, we're doing it and we will compensate people accordingly."

Compensation may be given in the form of an offset of debts owed to the bank in some cases.

"There are cases where we might owe someone money who has defaulted, or who still owes us a lot of money. Then it's a different matter. We'll just offset it against what they owe us. We won't be writing them a cheque," Aynsely added.

BankCheck, a Northern Ireland-based consultancy, which investigates bank errors for businesses and individuals, claims the Anglo’s estimates are too low, saying the overcharging could be as high as $250m. They also claim that the overcharging began before 1999 and continued after July 2004.

"I firmly believe that these percentages are understated and in effect the rate is somewhere between 0.125 per cent and 0.25 per cent. If we assume that his figures are correct the actual amount is somewhere between €200m and €400m. Furthermore, I believe that this practice started before 1999 and certainly did not stop in 2004 as suggested by Anglo," said BankCheck director Eddie Fitzpatrick.

The statute of limitations could theoretically mean Anglo might not be compelled to go back further than six years in compensating customers, but a legal source questioned by the Irish Independent said that the statute of limitations would begin to run from the moment the overcharging was discovered rather than when it began.

"In other words, if the errors or overcharging was spotted in the last couple of months the legal clock would start ticking from then. If the investigation being carried out by Anglo discovers that the policy of overcharging was deliberate then that is a different kettle of fish. There is no statute of limitations on fraud," said the source.