The High Court has refused to grant an order to Denis O'Brien directing a PR firm to reveal the identity of its client.
The businessman claims that Red Flag and its client, whom he wanted named, are involved in a conspiracy against him.
Denis O'Brien says he received a dossier of information about him, some of which he claims is defamatory.
Red Flag have admitted putting together the dossier, but maintain a duty of confidentiality to their client.
Judge Colm MacEochaidh said the file had not been published anywhere, and without publication, there could be no defamation.
