Serious tensions have developed between the Department of Transport and Aer Rianta over the progress of the investigations into claims that the Minister for Transport, Mr Brennan, left an unpaid bill of €5,000 for spirits and cigars over a decade ago.
It emerged last night that neither of the two reports into the potentially damaging allegations are likely to be published now until next week.
The Department of Transport last night wrote to Aer Rianta "insisting" that the company complete its inquiry into the unpaid bill by close of business today.
The letter was in response to a statement yesterday from Aer Rianta, in which it said its inquiry would not be finished until next week.
The Department maintains it cannot finish its investigation until the Aer Rianta inquiry is complete. It had initially been expected that both inquiries would be published today, with the Minister under pressure to have his name cleared of any impropriety.
The Department of Transport secretary-general, Ms Julie O'Neill, sent a terse letter by courier to the Aer Rianta board last night in which she said she wanted its report by this evening.
It is understood that the Department would even accept an interim report at this stage.
Sources confirmed that in the letter, Ms O'Neill demanded answers to a series of written questions she submitted to Aer Rianta on the matter last Monday.
The Department is not in a position to complete its own inquiry into the affair until Aer Rianta responds to these questions, sources added. "We have finished our side of the report now it is up to them," one said.
In a statement yesterday, Aer Rianta said the inquiry would not be completed until next week.
"The board has requested that the auditors to the company, KPMG, produce a report based on the inquiry," it said. "On completion the auditors will present its report to the board." A spokesman confirmed last night that a letter had been received from Ms O'Neill but refused to comment further.
However, the report is not expected today, despite the Department of Transport request. A special meeting of the Aer Rianta board will have to be convened when the report is complete next week.
Aer Rianta was yesterday still interviewing a number of key individuals and examining documentation from the period in question, 1989 to 1992.
Government sources believe the investigations would exonerate the Minister of any wrongdoing.
The Department is understood to have trawled through thousands of documents and has uncovered no invoice in its files for the goods in question.
Mr Brennan has said that to the best of his recollection, he "never personally received, authorised or had knowledge of the purchasing or delivery of the alleged goods referred to in the Sunday Independent article of Sunday last".
Aer Rianta is strongly opposed to proposals under consideration by Mr Brennan to take Cork and Shannon airports away from its control. There are also tensions over his decision to receive expressions of interest for the construction of a second terminal at Dublin Airport that would not be controlled by Aer Rianta.
The airports authority has denied that the story concerning Mr Brennan emanated from the company. An outgoing Aer Rianta director, Mr Dermot O'Leary, has backed up the report that a minister left a bill for drink and cigars unpaid.