Stanley says he wanted complaint against him referred by Sinn Féin ...

However, Mr Stanley later said in a statement through his solicitor, that the matter should have been referred to gardaí in September.

He said he raised "serious issues" last month and accused the party of a "character assassination". He said that he had first advocated for the matter to be sent to gardaí.

"The party should have referred it to the gardaí once both myself and my legal representative brought certain serious matters to the attention of the 'panel' on September 11.

“This complaint, which I refute, was lodged with the party on the very first day (July 26), that the 10-day nomination process opened for members such as myself to be put forward to contest the general election. In my case this had the effect of preventing me of having any hope of contesting it as a Sinn Féin candidate for Laois.

“It was received by Sinn Féin on the July 26 and I obtained written proof of this from them. Mary Lou McDonald has given wrong information by stating that it was only received on August 2. As a matter of fact, I made her aware in person on July 29 of it and that certain information regarding it had been circulated by party members."

This morning, Ms McDonald said: “I want to be clear here: I am not in a position to say whether or not the complaint or the counter-allegation meet the standard for criminal investigation. That’s not my job.  

“I am far happier that the complaint and the counter-allegation are now in the hands of the gardaí and they can do what they deem to be appropriate."

Ms McDonald said Sinn Féin’s investigation into the complaint, which was under the supervision of a barrister who was also a party member, concluded on October 4.

A “serious” counter-complaint surfaced during the process.

On Saturday, Mr Stanley confirmed he had quit the party. The Laois–Offaly TD, who also chairs the Public Accounts Committee, said he had recently been brought before a party inquiry, and that, due to its outcome, he would be resigning "with immediate effect".

Mr Stanley also claimed that the party inquiry had not been impartial.

“This ‘inquiry’ has been shown to have lacked any shred of credibility, not least due to a significant abuse of process. In many ways it resembled a type of kangaroo court. Legal examination of this matter will continue," Mr Stanley said.

In a statement on Sunday, the Sinn Féin leader insisted Mr Stanley's rights were protected throughout the inquiry process, saying he had a solicitor and a barrister with him at the meeting with the disciplinary panel.

Ms McDonald told RTÉ radio's Morning Ireland on Monday that both parties to the complaint — Mr Stanley and the complainant — were originally due to come back for comment on a preliminary draft on Monday morning but that Mr Stanley resigned in the interim.

She said she was first fully briefed on the matter after his resignation on Saturday night.

“The referral to An Garda Síochána was made in an abundance of caution, because I was not happy, nor would I be happy, with the party left with a serious complaint and a serious counter-allegation," she said. 

She said she does not personally know the “longstanding member of the party” who made a complaint against Mr Stanley.

Ms McDonald said she had been made aware of the existence of the complaint in early August.

However, she said she was not aware of the specifics of the complaint, claiming the whole investigatory process “is at arm’s length to the party”.

“I make no apology to anybody for the fair, impartial observance of the rules and standards of the party,” she said.

She also said the preliminary conclusions of a party investigation into the matter had made no final findings or recommendations, including whether or not the matter should be referred to gardaí.

Ms McDonald defended her party’s internal processes, saying “the buck does stop with me”.

Responding to queries about the resignation of Brian Stanley and two former Sinn Féin press officers, she said: “I am very much in charge of this party and, as the person with whom the buck does stop, I am absolutely insistent that rules and procedures are applied rigorously.

“I appreciate this is probably an unusual thing in Irish public or political life, that actually rules exist and rules are applied, and then the consequences and fallout of those rules becomes manifest, but that’s what you’re seeing here.” 

She told Morning Ireland: “I stand over the fact that our rules and procedures apply to everybody.” 

She added: “We are a party that is more than fit for government. We have procedures that work, that holds people to account, and, let me say, in my opinion and in my experience, there has been far too little accountability in Irish public life and in Irish political parties.

“You see under my leadership, without fear — and I will not be cowed on this point — the rules get applied, the processes are respectful, they protect everybody’s rights.

“But where the behaviour falls beneath standards, where there has been wrongdoing, people will face the consequences for it.”

In his statement today, Mr Stanley said “the information had been deliberately kept from me that there was a complaint or the nature of it". 

"An "omerto"[sic] was in place. One middle ranking party member instructed other members that I was not to be informed of its existence. In actual fact I had to get my solicitor, six days later, to write to the party (31 July) to ascertain what was the nature of this complaint. 

 “In the intervening period ie from July 26, the process of character assassination was well underway by a certain party clique and has continued unabated since then. These facts and others mean that there has been a significant abuse of process and when it was brought to the attention of the Sinn Féin "panel" it was simply brushed aside,” he said.

“I stand over what I stated two days ago regarding what the party refer to as an "inquiry".

Mr Stanley is the second Sinn Féin TD to leave the party recently. On Friday, Kildare South TD Patricia Ryan confirmed she had resigned from the party.

Meanwhile, the Tánaiste questioned whether the complaint into Mr Stanley should have been passed onto gardaí earlier.

Speaking in Luxembourg, Micheál Martin said it would be up to Sinn Féin to provide “greater clarity” on the matter.

Timeline of events in complaint against Brian Stanley 

August 2 or July 26: Sinn Féin says statement from complainant against Brian Stanley received on August 2 - Mr Stanley disputes this date and says it was received by the party on July 26 and he discussed it with Mary Lou McDonald on July 29 

August through September: Preliminary inquiry process ongoing, during which time a "serious" counter-complaint surfaces; 

October 4: Preliminary inquiry process concludes, with findings written up and sent to both Mr Stanley and the complainant;

October 12: Brian Stanley resigns, and Ms McDonald fully briefed on inquiry process for the first time; 

October 13: Matter referred to gardaí.

— additional reporting from PA