At his press conference last weekend, Taggart was critical of RTE, its highly respected chief news reporter Charlie Bird and the Irish Examiner for its reporting of recent events. And it is understood that he has now asked his legal advisers to issue proceedings, claiming defamation of character, against both media organisations.

It is understood that a decision last Tuesday by TG4 to pull a five-minute report on last weekend's press conference from its weekly programme Greyhound Viewwas the "final straw" for Taggart.

TG4 management decided that including the segment on the press conference would be inappropriate and would run counter to TG4's public service remit. It said the press conference was covered extensively on its news programme and the station "felt that was the best place for it to be covered".

Taggart is said to have been angered by the decision and is now determined to press ahead with his legal action against RTE.

The investigation by former justice department secretary general Tim Dalton into a decision by Bord na gCon's control committee not to publish two positive tests for banned substances is expected to be completed early next month. The inquiry was triggered by a dispute between Taggart and the recently departed Bord na gCon chief executive Aidan Tynan.