Dr Sean O'Domhnaill, a patron of the No to Nice Campaign, yesterday failed in his High Court action seeking an injunction against the Taoiseach, Mr Ahern.
He had sought the injunction restraining Mr Ahern from repeating remarks he had made at the weekend in relation to the funding of the No to Nice cam paign.
Mr Justice Murphy held that Dr O'Domhnaill, who is employed by the Department of Health in the National Drug Treatment Centre, Pearse Street, Dublin, was not entitled to an injunction and awarded costs against him.
Mr Ahern was represented by Mr Sean Ryan SC and Mr Eamonn Leahy SC.
Sources outside the hearing estimated that legal costs for overnight preparation and the court appearance could cost Dr O'Domhnaill in the region of £20,000 for his halfhour in court.
For the Taoiseach, Mr Ryan told the court Mr O'Domhnaill had failed to prove that the alleged remarks had identified him or referred to him or that he had suffered any damage as a result of their publication in the media. He had also failed to prove the remarks were defamatory of him.
Mr O'Domhnaill had claimed the Taoiseach had made untrue and erroneous allegations relating to him and leaders of the No to Nice Campaign over funding and had linked him with right-wing fundamentalists in the US.
Mr Justice Murphy said it was significant that Dr O'Domhnaill had not been identified in the speech made by the Taoiseach in Killarney or in reports of the speech published in the press.
He had sought to identify himself with the remarks by referring in his affidavit to the court that he was a patron of the campaign. The judge felt that no jury reading the published articles could in any way associate Dr O'Domhnaill with the articles or the Taoiseach's reported remarks.