Denis O'Brien has failed in his bid to have the identity of a PR firm's client revealed.

The businessman sought a High Court order to compel Red Flag to name the client who had commissioned a dossier of information about Mr O'Brien.

Mr O'Brien alleges that the dossier is part of a conspiracy against him involving Red Flag - a PR firm whose executives include former executives at Independent News and Media (INM).

Judge Colm MacEochaigh said that because the dossier had not been published, there was no defamation and no proof of damage to Mr O'Brien.