Mary Lou McDonald said she has written to the young person who received inappropriate texts from a former Sinn Fein senator, expressing her “deep regret” over a statement she made following his resignation.

The Sinn Fein leader said that ex-senator Niall O Donnghaile has faced consequences for his behaviour, including the end of his political career and his membership of the party.

She said that for “someone like him”, those are big sanctions.

The Dublin TD said the statement made following Mr O Donnghaile’s resignation should not have been made as it caused “hurt” to the young person.

Mary Lou McDonald speaks during a press conference at the Clayton Hotel in Dublin, during the launch of their new health policy (Niall Carson/PA)

“I wrote to the young person at the heart of this matter and expressed to them my very deep regret and my sorrow that I had caused them pain or distress by the commentary that I made on Niall’s exit,” Ms McDonald said.

“That’s the last thing I would do. Apart from being a politician, I’m a mother and I know something about raising young adults, so I deeply regret that, I’ve expressed that to the young person. And I mean it. I meant it and I mean it.

“The matters around Niall were referred to the PSNI, to social services. That was necessary. That was the most important thing, actually, because when something like this comes to the attention of any organisation, your first responsibility is to ensure that the relevant statutory authority is across this, because that’s actually how you action safeguarding in the first instance.

“Then Niall faced consequences. His political career is over. His membership of Sinn Fein is over. And for someone like him, those are big sanctions. I was conscious at the time that he was in mental health crisis.

“I do not offer that as an excuse for his behaviour, nor was it an excuse. He faced accountability and consequences, that had to happen.

“But I was concerned. We were concerned about his frame of mind and his safety, and therefore the logic of the manner of handling.

“Of course, with the benefit of hindsight, the statement shouldn’t have been made and I say that because it caused hurt to the young person question, that’s my concern.”

Earlier this month, former Sinn Fein senator Mr O Donnghaile revealed the reason he stepped down from Seanad and left the party last December was due to a complaint that accused him of sending inappropriate text messages to a teenager.

Sinn Fein referred the matter to the PSNI and social services last September, but no criminal investigation was undertaken.

Ms McDonald rejected questions about whether Sinn Fein had been leaving the door open for Mr O Donnghaile to return to the party at a later stage if the allegations around his behaviour had not surfaced.

She made the comments as the party launched their new health policy.

She added: “When somebody breaches trust in the way that he did and acted inappropriately, although I have to emphasise, not criminally, inappropriately, there is no door back from that.

“I think if you look to my actions as party leader, not just in this case, but in others where action has been necessary and where sanctions were necessary, I have not flinched.

“Those actions have been taken and those sanctions have been delivered. And our organisation is no different to any other. You have your procedures. You cannot legislate for human behaviour, unfortunately. But the question is, when it comes to light that you have robust procedures to deal with them. But, no, there was never any question of that at all.”

Meanwhile, Ms McDonald defended the party’s handling of a complaint made against high-profile Sinn Fein TD Brian Stanley.

Brian Stanley resigned from Sinn Fein earlier this month (Niall Carson/PA)

The Laois TD resigned from the party weeks ago amid a controversy relating to the complaint.

He has claimed he was subjected to a “character assassination” by a clique within the party and likened its processes to a kangaroo court.

A number of reports over the weekend published contents from the party’s draft report into the complaint and counter-allegation made by Mr Stanley.

“The initial complaint, and then the secondary allegation, as I set out in detail, were dealt with by the book, utterly, appropriately and respecting everybody’s rights to process, to fair play. It was, of course, a confidential process,” she added.

“I understand that material you have it, that did not come from us, and it would not be appropriate, actually, for me to make any further commentary.

“That was those of you that have whatever you have, just bear in mind that that was a draft report. The process wasn’t completed because, of course, Deputy Stanley resigned.

“We have dealt with it appropriately. We have dealt with it fully and we took the decision, which I presume you now understand, to refer matters to An Garda Siochana.

“We have now discharged all of our responsibilities fully.”

Ms McDonald said the party’s rule book was “applied without fear, without favour”.

“The rules apply, whether you’re a grassroots member or a parliamentarian with decades of service. That’s what happened,” she added.

“Brian Stanley’s bad behaviour is a matter for him. I’m not responsible for that and I will not take responsibility for that.

“What I am responsible for as the leader of the party is the investigation and inquiry into a complaint such as that when it’s made, and it was done by the book.”

The party will run a candidate in the Laois constituency, with a selection convention to be held in the near future.