AIB, Bank of Ireland and a number of other state-backed institutions will have to repay €100m they "systematically" ripped off from ordinary customers during the boom years, the Sunday Tribune can reveal.

The country's two biggest banks and at least two other institutions covered under the bank guarantee scheme face new overcharging investigations on foot of fresh evidence provided by at least two new whistleblowers to the Financial Regulator.

Michael Moynihan, the chair of the Oireachtas Economic Regulatory Affairs Committee, which has led the counter attack on overcharging by banks, said he is aware the Financial Regulator has received "a huge amount" of new dossiers and is actively investigating explosive new allegations of overcharging.

Significantly, he said, regulator Matthew Elderfield has been directly provided with new evidence by at least two new whistleblowers who have detailed a level of overcharging across the leading lenders of "an extraordinarily extravagant" scale. The whistleblowers have provided scores of documents to the authorities of "systematic" and as yet uncovered abuses.

"All the records of overcharging will be looked at and each institution will be examined," said Moynihan, Fianna Fáil TD for Cork North West.

"I believe that the new overcharging has been over a wide range of accounts and over a wide range of systems. The new cases show, in my opinion, a pattern of deliberate and systematic overcharging by the banks," he said. The level of repayments speaks of an extraordinary level of "deliberate" overcharging that cannot be explained away by normal day-to-day banking errors.

According to Central Bank records, the Irish financial services industry repaid €180m to ripped-off customers in the past decade, including €88m repaid so far by AIB alone.

"It is across the banks," said Moynihan. "The charging costs will be shared almost evenly between the lenders without any single bank contributing the lion's share. This means that the level of new overcharging was huge." Permanent TSB is not implicated in the new dossiers, it is believed.

"I understand that the regulator is going to examine files of overcharging in all the financial institutions. And I believe that there are also far more serious issues involving overcharging than have come to light at present. I believe there will be further repayments by financial institutions. I believe that there will be further substantial repayments which have not come to light when the institutions are thoroughly investigated and I believe the repayments could be as much as €100m," he added.

A spokeswoman for the Financial Regulator said: "Overcharging is a high priority for the organisation and we are working with firms to ensure that errors are corrected and refunds made."