Fianna Fáil leader Micheál Martin stepped up his criticism of Sinn Féin's handling of the Máiria Cahill controversy yesterday and expressed his shock at the disinterest shown by the "modern faces" in Sinn Féin in finding out what happened.

He said some of the revelations from Ms Cahill about an alleged cover-up of sexual abuse had been shocking. “What is even more shocking has been the disinterest of the so-called modern faces in Sinn Féin to finding the truth,” he said. “They are happy to collude in an approach which again seeks to undermine the victim.”

Mr Martin said the measure of a republic was how it treated its weakest citizens and the measure of true republicans was how they put the interests of citizens ahead of those of party and faction. “By any measure, Sinn Féin is failing even the most basic standards of republicanism.”

Mr Martin said few things were as striking as the IRA’s insistence on enforcing discipline in everything. “There is no diversity, there is no dissent. No matter how appalling the action there is a vow of omerta taken even by its youngest members,” he said.

“Justifying the movement is always the number one priority and it still seeks to crush and marginalise anyone who breaks their silence. If you sign up for their movement the first thing required is not that you support their policies it is that you justify their history and stay quiet about their darker elements.”

Mr Martin was speaking at Fianna Fáil's annual Wolfe Tone commemoration at Bodenstown, Co Kildare, yesterday. He said it was not the place to go into the issues in depth but "the incredible personal bravery which it takes to speak out deserves all of our respect and support".

Asked afterwards if his focus on Sinn Féin had anything to do with the party’s good showing in recent polls, he said the Máiria Cahill case had come to his attention two years ago, long before any polls. She had approached him and he said he was taken aback at the gravity of her story.

He said it was particularly shocking that Sinn Féin would seek to marginalise someone who spoke out and try to marginalise her credibility. There was “an absolute absence of any dissent within the Sinn Féin organisation itself, any freedom of thought or action here, I think it’s an unhealthy dimension to that party’s affairs”.