The Taoiseach says he hasn't ruled out an external criminal investigation into the alleged smear campaign against Garda Whistleblower Maurice McCabe.

Enda Kenny told RTÉ's This Week programme that while it might be necessary, the Commission of Investigation first has to determine whether a crime was committed.

He also said that he did not ask Katherine Zappone about the details of her meeting with Sergeant McCabe as she met him in a "private capacity".

Earlier, Sergeant McCabe rejected the apology released by the HSE yesterday, on the basis that he did not accept that the allegations in his file were created in error.

There have been repeated calls for an external criminal investigation to take place, as opposed to or alongside the Commission, given that the Gardaí are involved in the scandal.

Kevin Doyle, Political Editor with the Irish Independent, says this might be a good idea: