Taxpayers will have to pay up to half a billion euro to developers and other customers of Anglo Irish Bank who were overcharged in the last decade, the Sunday Tribune has learned.

Eddie Fitzpatrick, director of Bank Check, said the Anglo bill alone would be at least three and as much as 10 times the €30-€50m range calculated last month by Anglo's new boss Mike Aynsley.

Bank Check has retrieved €16m for customers who were levied unjust fees and interest charges by the main Dublin banks over the last 14 years. Fitzpatrick said the scale of overcharging by Anglo and the main general lenders, including AIB, Bank of Ireland and Permanent TSB, continues to be downplayed by regulators.

Bank Check, which is representing several Anglo customers, said its offer to Anglo to tap its expertise was turned down in recent weeks by Aynsley.

"It will be another public relations disaster for Anglo and the government if they get their figures wrong. If it is the regulator or an outside accountancy firm that does the independent analysis, well, frankly, they do not have a clue," said Fitzpatrick.

He added that the new regulator was still using rules and flawed methodology left over from failed predecessors in assessing overcharging cases.

The examination of overcharging of Anglo customers, which has excited the interest of web blogs, including well-informed anonymous contributors to the Guido Fawkes blog, ranges from the largest and now insolvent property developers to the smallest shop owner customer of the now state-owned bank before 2004. But taxpayers will pick up the huge bill, Fitzpatrick said.

His warning comes after the Sunday Tribune revealed last week that Michael Moynihan, chair of the heavyweight Oireachtas Economic Regulatory Affairs Committee, had collated dossiers of new evidence and testimonies that pointed to "systematic" overcharging and rip-offs of ordinary customers amounting to €100m by AIB, Bank of Ireland and other state-aided general lenders for almost two decades. Moynihan's dossiers do not include overcharging already admitted by Anglo.