Businessman Denis O'Brien has lost his appeal over the High Court's refusal to make orders directing Red Flag Consulting to give him documents that might disclose the identity of its client for a dossier about the businessman.

Mr O'Brien's counsel Michael Cush SC had argued he is entitled to know if the client is the businessman's "absolute sworn number one enemy in the world".

It was argued that Mr O'Brien needs the client's identity for proceedings over the dossier, which he alleges contains defamatory material about him.

But the Court of Appeal has dismissed Mr O'Brien's appeals over the High Court refusal of discovery.

It also dismissed a cross-appeal by Red Flag against orders requiring it to disclose documents relating to communications between it and the client.

Court of Appeal president, Mr Justice Sean Ryan, sitting with Mr Justice Michael Peart and Mr Justice Gerard Hogan, said the businessman's claim in his case against Red Flag is one of conspiracy to damage him in a variety of ways, including defamation.

His claim was pleaded in conspiracy, causing loss by unlawful means, and defamation, and he was seeking damages, including exemplary damages.

The judge said the fundamental point is Red Flag's client was entitled to have the dossier prepared, "even if this was done for the basest of motives".

That in itself was not sufficient to establish a conspiracy on the part of that client, or to demonstrate that Red Flag itself was a co-conspirator with the client.

If the dossier was actually published by Red Flag, and it has defamed Mr O'Brien, then he had a remedy under the Defamation Act 2009, he said.

Mr O'Brien was not entitled, on the law, to ascertain the identity of that client by means of seeking discovery from Red Flag, he ruled.

The High Court had correctly refused this discovery application having regard to an earlier application by Mr O'Brien aimed at getting the client's identity.

That earlier application was a "legitimate" application and was one that had been considered and refused by the High Court.

After the judgment was handed down, Frank Beatty SC, for Mr O'Brien, said his client would consider whether to seek permission to appeal the Court of Appeal decision to the Supreme Court.

Because the main appeals were by Mr O'Brien, and Red Flag's cross-appeal was "relatively insignificant", the judge said the court had decided to award costs against Mr O'Brien, with a stay on payment pending the final determination of the case.

If there was any objection to the costs order, submissions could be filed on that within four weeks, he added.

When Mr Beatty said he was anxious an imaging order aimed at preserving material from devices of Red Flag should remain in place, Mr Justice Ryan said that was not a matter before the Court of Appeal but he believed it would be unwise to rush to alter the current position.

Michael Collins SC, for Red Flag, said he understood the imaging order continues until all appeals are exhausted and Mr Beatty had signalled a possible application to the Supreme Court.

In his appeal, Mr O'Brien claimed the dossier was compiled for the "hostile" motive of damaging him and he disputed Red Flag's claim it prepared the dossier in the ordinary course of business for a client whose identity it is entitled to keep confidential.

In opposing discovery, Red Flag argued Mr O'Brien was engaged in a "pure fishing expedition" and could in law seek a document that would disclose the identity of a client to see if the identity is relevant.

The High Court found Mr O'Brien had failed to show the client's identity was relevant and necessary for his case against Red Flag.

Mr O'Brien had sought the documents for his action against Red Flag alleging defamation and conspiracy in relation to certain contents of the dossier including concerning the Siteserv sale and his charity activities in Haiti.

He also said he needs the documents to consider whether to also sue the client.

Red Flag denies defamation or conspiracy, denies Mr O'Brien had been harmed or suffered loss and has also raised issues about how he got the dossier.

He has claimed he got it anonymously from a USB stick placed in an envelope left in his Dublin offices in October 2015.