Denis O’Brien has lost his latest attempt to establish the identity of a person who commissioned a dossier of material he believes to be defamatory.

It is part of his legal action against Dublin PR firm Red Flag Consulting.

The businessman believes he is entitled to know whether the client is a sworn enemy of his - because it could determine motivation.

A High Court judge previously ruled that the identity of Red Flag’s client wasn’t relevant to proceedings, and Mr. O’Brien appealed that decision.

In ruling against him today, the Court of Appeal said the client was entitled to have the dossier prepared, even if it was done for the 'basest of motives.'

The judgement goes on to say the commissioning of such a dossier in itself isn’t enough to establish a conspiracy.