Not making all members of the Oireachtas banking inquiry immediately aware of allegations of wrongdoing was a "major mistake", according to Fianna Fail TD Michael McGrath.

A whistleblower has made a series of claims against the investigation team at the committee including potential conflicts of interest and special treatment of some witnesses.

The allegations were made to some members, including the chairman Ciaran Lynch in April, but other members of the inquiry were not made aware of the claims until last week.

Mr McGrath said he only became aware of the allegations last Tuesday when he received a letter from the whistleblower.

He said: “It was a material fact that should have been brought to our attention. Allegations were made that were very serious in nature and which needed to be investigated.

“To learn as we did a number of months later from the whistleblower is not a good way to do business.”

Mr McGrath said he has not received a copy of the 82-page document from the former investigator with the inquiry.

He said an independent investigator needed to be appointed to ensure the allegations were dealt with thoroughly.

Mr McGrath said they should be dealt with by the end of August so hearings can continue in September.

The inquiry is due to meet in private session this afternoon.

An investigator, who worked with the inquiry until recently, has submitted an 82-page document under the Protected Disclosures Act claiming wrongdoing at the committee.

The correspondence, which was sent to some members in April, makes a series of allegations about the investigation team hired by the inquiry.

The Irish Times has learned one of the claims alleges that a senior investigator dined with a witness “days before the representatives of the participant appeared before the joint committee”.

The whistleblower also alleges preferential treatment was given to the Central Bank, the Department of Finance and, to a lesser extent, the National Asset Management Agency (Nama).

The document alleges the provision of false information to the committee and the inappropriate management of potential conflict of interests by lead investigators.