Mr Dermot Quigley has interviewed the chairman of the Office of Public Works, Mr Seán Benton, as part of his inquiry into the awarding of contracts to Ms Monica Leech by Mr Martin Cullen.
Mr Quigley, former Revenue chairman, has also spoken to senior officials in Environment, Mr Cullen's former Department, and is expected to report to the Taoiseach later this month.
A spokesman for the Minister would not say whether Mr Quigley had spoken to Mr Cullen.
Mr Ahern asked Mr Quigley to examine the circumstances in which Departments under Mr Cullen's direct political control gave lucrative public relations contracts to Ms Leech, a friend and political supporter of Mr Cullen.
While Mr Quigley has not been given a deadline for his report, the Taoiseach said on December 22nd he hoped the inquiry would be completed within a month. Mr Quigley was asked to report on the awarding of the contracts, and to make recommendations on "any changes in practice which may be desirable".
Criticism of Mr Cullen in the report would raise doubts about his Cabinet future, but he says he is confident it will not reflect negatively on him. The report could become a major point of controversy when the Dáil resumes on January 26th.