The Supreme Court has begun hearing an appeal by The Irish Times editor and a journalist against a High Court order requiring them to answer questions from the Mahon Tribunal.

The tribunal wants to ask editor Geraldine Kennedy and journalist Colm Keena about the source of an article about payments to former Taoiseach Bertie Ahern when he was Minister for Finance in 1993.

A stay on the High Court order permitting the questioning remains in place pending the outcome of the appeal.

In October 2007 the High Court ordered the journalists to answer questions from the tribunal about the source of the article, written by Mr Keena and published in The Irish Times on 21 September 2006.

The tribunal claimed the article was based on a confidential letter it sent to businessman David McKenna during its private investigative stage.

In its judgment, the High Court ruled The Irish Times' privilege against disclosure of sources in the case was 'overwhelmingly outweighed' by the 'pressing social need' to preserve public confidence in the tribunal.

As that could only be done by the tribunal asking the journalists questions, the court said it believed the orders sought by the tribunal were necessary in a democratic society.

The court also stressed its decision must be seen in the circumstances of the particular case where the answers to the questions were unlikely to reveal the source.

If the questions could lead to identification of the source then the journalistic privilege against disclosure could be invoked, the court said.

This morning lawyers for The Irish Times described this part of the High Court ruling as 'illogical' and said it did not follow that because a person did not know the source they could not assist in the idenfication of the source.

The court was told that the tribunal's intent in the asking of questions was to exculpate itself as the source of a leak but in doing so the field would be significantly narrowed and sources could be identified by a process of elimination.

However, lawyers for the tribunal said the case being argued related to the relationship between a journalist and a source and the trust cultivated in that relationship.

This could not hold the same weight as a source who did not trust the journalist with its identity and had chosen to retain its anonymity.

The tribunal's legal team said it would seek to draw a distinction between a source anonymous to the journalist and a source known to the journalist.

The case continues tomorrow.