A spokesman for Denis O'Brien has said the businessman intends to appeal a High Court ruling refusing to order a public relations and lobbying firm to disclose documents which would reveal the identity of a client who directed it to prepare a dossier about him.

Mr O'Brien began legal action against Red Flag Consulting, its chief executive, Karl Brophy, chairman Gavin O'Reilly and three other members of staff last year.

He claimed they were involved in a conspiracy to harm his interests and said they compiled and wrote material in a dossier about him on the instructions of a client.

He claims the material in the dossier is defamatory of him.

Mr O'Brien said he had received the dossier, anonymously, on a memory stick in an envelope, in his office in Dublin.

The High Court also ruled it was "surprising" that Mr O'Brien had not been able to provide any information at all about how the memory stick came to him, or why he had no information about its "mysterious appearance."

The defendants admitted they had produced the dossier - which contained some original documents and a number of articles from various media organisations.

But they said it was not compiled to further any conspiracy against Mr O'Brien or to damage his interests.

Mr O'Brien sought the disclosure of documents which would reveal the identity of Red Flag's client.

His lawyers claimed revealing the identity of the client would demonstrate that the client's motivation was to injure Mr O'Brien.

But Mr Justice Colm Mac Eochaidh ruled the identity of the client was not relevant to Mr O'Brien's action against Red Flag.

He said there was no doubt that the motivation of the defendants in producing the dossier was a major issue in the case. But the judge said knowing the client's identity may be of great use to Mr O'Brien or it may be wholly irrelevant.

And he said no basis had been established as to why, if the motivation of Red Flag's client was mischievous, then the mischievous motivation was shared by Red Flag.

He said the most Mr O'Brien had been able to say was that gaining the client's identity might assist with proving the client's motivation, which in turn might assist in attributing that motivation to Red Flag in compiling the dossier.

Mr Justice Mac Eochaidh said this fell short of what was required by Mr O'Brien in this case.

The judge also ruled that Mr O'Brien was not entitled to documents disclosing the identity of those to whom the dossier was sent. Mr O'Brien claims the dossier was defamatory and was "published" to others.

The judge said Mr O'Brien had admitted his claim in relation to publication "lacked specificity" but had said the "clandestine nature" of Red Flag's activities was the reason for this.

Mr Justice Mac Eochaidh said he had ruled a year ago that he had not been persuaded that there was any evidence for him to be certain that there had been any publication. And he said Mr O'Brien had not provided any additional information in this application to persuade him to change his view.

Mr Justice Mac Eochaidh added that Mr O'Brien had failed to substantiate a claim that questions posed to him by journalists in the run up to this action last year, indicated that the journalists had seen the dossier.

He said Mr O'Brien had not given any details at all of examples of the questions asked or the identity of the journalists asking the questions.

The judge said this was "surprising" because Mr O'Brien had claimed it was the activities of the journalists that had aroused his suspicion that there was a conspiracy against him. The omission of these potentially very relevant facts was "odd", the judge said.

The judge said it was also surprising that Mr O'Brien had not been able to provide any information at all about how the memory stick came to him.

He said Mr O'Brien had not even told the court why he has no information about the mysterious appearance of the memory stick. He said he would not order the disclosure of documents in relation to publication of the dossier because of the absence of information from Mr O'Brien on this issue.

Mr Justice Mac Eochaidh said if Mr O'Brien was entitled to the discovery of evidence without which his case would fail, then every plaintiff who believed he or she had a good case, but lacked the evidence to prove it would also be entitled to such discovery.

He said this would lead to litigants flooding the courts with unsubstantiated claims, hoping that applications for the disclosure of documents would produce the evidence they lacked.

The judge ruled Mr O'Brien was entitled to communications between the defendants and their client as these would reveal the nature of their relationship.

But he said the disclosure should be limited to communications relating to the dossier and/or to Mr O'Brien.

He said that any disclosure ordered in this category could be redacted to conceal anything which may disclose the identity of the client.

The case will be back in court again next month, when costs and other issues will be dealt with.