CI╔ yesterday claimed it had no knowledge of a "letter of intent" to Esat which was cited three times in the telecom firm's flotation prospectus in 1997.
The transport group's solicitor, Mr Michael Carroll, told an Oireachtas inquiry that there was no trace of the document, which was referred to in evidence by the businessman Mr Denis O'Brien, Esat's former chairman.
Mr O'Brien also claimed at the hearing that the inquiry's chairman, Mr Seβn Doherty TD, was unfit for the post because of his links to a phone-tapping scandal in the early 1980s. Mr Doherty described the claim as "outrageous".
The inquiry, by a sub-committee of the Oireachtas Joint Committee on Public Enterprise and Transport, is investigating a £36 million overrun on a CI╔ signalling project.
It has heard claims that work on a parallel telecom system for Esat undermined the signalling project, which is still incomplete.
Esat had yet to reach agreement with CI╔ when its prospectus was published, but said it expected to use the group's rights of way to construct a backbone telecom network "based on a letter of intent".
Mr Carroll said that the existence of such a letter would have "very serious implications" in the context of CI╔'s agreement with Esat.
He told the inquiry: "There at least seems to be a suggestion that there is in existence a document which may have legal significance, of which I was unaware throughout the negotiations and throughout the process of putting formal agreements in place."
The prospectus described the proposed system, 1,950km in length, as a "national backbone fibre-optic network covering all major Irish cities".
But Mr O'Brien denied suggestions that Esat's plans to construct the system were a cornerstone of Esat's flotation on the Nasdaq stock exchange in 1997.
This was disputed by Mr Carroll, who said the system had to have significance because it was part of the infrastructure Esat was offering as part of its package.
Mr Carroll said: "Mr O'Brien tended to play down the importance of that. That is not how it comes across at least on a quick run through the document.
"This seems to be one of three bullet points that recur on three different occasions in support of the value of what's being offered in exchange for some $78 million of punters' funds, so to speak."
Mr Carroll said he would consult Esat's legal team to get to the bottom of the matter.
Mr O'Brien declined an opportunity to withdraw his comments about Mr Doherty, who was minister for justice in a government led by Mr Charles Haughey 20 years ago. He declined to comment when asked whether the remarks were calculated; he published them in a press statement about 30 minutes after leaving the inquiry yesterday morning.
Mr O'Brien accused Mr Doherty of posing a "disgraceful" question on Wednesday when he had asked whether Esat's agreement with CI╔ was a "sweetheart deal".
