A central Bank official claimed his superiors in 1988 ignored his concerns about the existence of loans backed by offshore deposits within Guinness & Mahon, the tribunal has heard.
Mr Terence Donovan, who is currently deputy head of bank supervision with the Central Bank, told the tribunal he refused to sign a report into Guinness & Mahon in 1988 because it would omit his concerns.
These claims will be strongly contested by other bank officials.
Mr Donovan was a trainee in 1988. He had recently transferred to the supervision department. The onsite inspection of Guinness & Mahon was his first investigation.
During the inspection, he found terms he did not understand, which indicated that Guinness & Mahon was securing loans with Cayman Island funds. At the time, he thought these facts were significant, but he acknowledged this could be because he was new to the job.
He raised these concerns with his superiors in the bank, but he said he did not receive satisfactory answers. "I was not prepared to sign because I felt the report was deficient in the issue of Guinness & Mahon back-to-back loans," he said.
He also met senior officials in Guinness & Mahon - Mr Martin Lanigan O'Keefe, and Mr Michael Pender, the managing director.
Asked by them if he felt the matter should be the subject of further investigation, Mr Donovan replied "yes".
Mr Donovan also said he felt full information was not being provided to the Central Bank by Guinness & Mahon.
He said he felt there were inconsistencies between information provided by different sources within Guinness & Mahon. He told the tribunal that aspects of the operation of Guinness & Mahon, which may have involved back-to-back loans were not being pursued because they were regarded as sensitive.
Mr Donovan told the tribunal, however, that he was "at no time in possession of definite evidence of tax evasion" in Guinness & Mahon.
He also said he had not come across any evidence of a "bank within a bank" as the secretive Ansbacher deposits scheme is sometimes described.
Mr Donovan said he brought his findings to the attention of other members of the Central Bank, including Mr Adrian Byrne and Mr Brian Halpin, neither of whom has any recollection of having any dealings with Mr Donovan about his concerns regarding back-to-back arrangements in Guinness & Mahon.
Fearing his working relationship with his superiors would be damaged because of his refusal to sign the report, he asked for a transfer, seeking advice from Mr Michael Deasy.
Mr Deasy said he had no recollection of any such approach from Mr Donovan.