The former leader of Sinn Féin Gerry Adams has asked the High Court to order the BBC to hand over more information in relation to a defamation case he is taking against the broadcaster.
Mr Adams is suing the BBC over a 2016 BBC Spotlight programme.
He claims he was defamed by a false allegation in the programme that he had sanctioned the killing of former Sinn Féin official, Denis Donaldson, who worked for decades as a spy for MI5.
The BBC denies defamation. The corporation says it can provide certain research materials used in the making of the programme, but it says other categories of documents sought by Mr Adams are too broad.
Mr Adams claims he suffered damage to his reputation as a result of what he says is a false allegation made by an anonymous source that he sanctioned the killing of Mr Donaldson.
Mr Donaldson was shot dead at his home near Glenties in Co Donegal in April 2006.
The allegation was made in the programme by an anonymous source, known as "Martin", who claimed he was also a paid State agent, as well as being a member of the IRA.
Lawyers for Mr Adams said the material provided by the BBC so far was too vague and inadequate.
The BBC claims the programme was put out in good faith and during the course of a discussion on a subject of public and vital interest and that it constituted responsible journalism, which was the result of careful investigation.
Lawyers for the BBC said it was willing to hand over material in relation to research and materials used in the making of the programme, but was not prepared to go beyond that.
Senior Counsel Paul Gallagher said one of the categories of material sought by Mr Adams was so broad that would involve oppressive and onerous searches of material in the BBC's huge archive.
Mr Justice Charles Meenan reserved his decision on the issue.