Lawyers for businessman Denis O'Brien have said they want their IT experts to have access to all computers and devices controlled by a public relations consultancy firm which Mr O'Brien alleges is involved in an unlawful conspiracy against him.

Mr O'Brien's lawyers told the High Court today they believed the order made by the court last week allows them to take forensic images of all computers and devices used by Red Flag Consulting, its Chief Executive Karl Brophy, Director Gavin O'Reilly, and other members of staff.

Mr O'Brien alleges Red Flag was involved in creating a dossier about him, which he says was created and disseminated to cause him harm.

The court heard Mr O'Brien's experts have not been given access to Mr O'Reilly's computers.

Lawyers for the defendants say Mr O'Reilly is a non-executive director and had no hand, act or part in the creation of the dossier and has only accessed Red Flag's computer system once, in 2014.

The defendants' lawyers say the court's order extended only to devices used to store or contribute to the dossier and not to all computers used by all members of Red Flag's staff.

Senior Counsel Michael Collins said if Mr O'Brien was seeking a wider order, then he wanted Mr O'Brien's lawyers to put before the court the grounds on which such an invasive and remarkable order was being sought.