Proceedings were dramatically delayed and the court cleared as the remark by Naomi Long, leader of the cross community Alliance Party and now an MLA, was discussed at Belfast Crown Court.
Launching a legal bid to have the jury discharged, Frank O’Donoghue QC, representing Stuart Olding, who was acquitted of rape, said the trial was on a “knife edge”.
The lawyer said: “This is the straw that has broken the camel’s back in this case.”
The revelations are only being made public after reporting restrictions were lifted by Judge Patricia Smyth at Belfast Crown Court on Wednesday.
Ireland and Ulster fly-half Paddy Jackson, 26, and team mate Stuart Olding, 25, were unanimously acquitted of rape by a jury which deliberated for three hours and 45 minutes having heard all the evidence in a nine-week trial.
Jackson was also found not guilty of sexual assault.
Both men had strenuously denied all allegations against them.
The court heard Ms Long had been critical of comments in Mr O’Donoghue’s closing speech in which he described “middle class girls” who were in the house at the time of the alleged rape.
Ms Long posted on Twitter: “I genuinely have no words for how atrocious this statement is.
“Middle class girls?
“What? Because “working class girls” wouldn’t care/don’t matter/think rape is normal?
“What is the implication of that comment even meant to be?
“Appalling at every level.”
The comment was re-tweeted 36 times and received 277 likes, the court was told.
It was posted at a crucial point in the marathon trial after all of the evidence had been heard and as Judge Patricia Smyth was issuing her legal direction to jurors on day 40 of the 42 day case.
Mr O’Donoghue argued the post risked prejudicing the administration of justice and had the capacity to reflect adversely on Olding.
He said: “I was frankly aghast to find that Ms Naomi Long had taken it upon herself, notwithstanding that she has had no involvement in this case, has never attended the trial and has no obvious connection to this trial, to tweet an opinion to her followers about the appropriateness of my use of language during the course of my speech.”
The lawyer further suggested that as leader of Northern Ireland’s “third largest political party” Ms Long was someone of “extraordinary high profile” and influence.
He said: “However, given her profile as a leader of a mainstream political party, a Belfast MLA, the fact that she is a woman speaking about male attitudes to rape in the context of this trial means that there is a reasonable prospect that her views will have been received by one or more than one member of the jury.
“I do not know anything about the members of the jury. Further, in purely numerical terms, Alliance has approximately 10% of the vote in NI.
“It is the third largest party in Belfast. It is reasonable to assume, therefore, that at least one member of the jury may be inclined to vote Alliance or to see Naomi Long and her party as someone whose opinions carry weight and influence.
“In our view, the line has now been crossed.
“This Court has an obligation to ensure that an accused person receives a fair trial. The Court has done its utmost to discharge that obligation.
“The trial is on a knife edge. The jury is just about to go out to consider its verdicts. The timing of Ms Long’s opinion on social media could not be more unfortunate, to put it mildly.”
The lawyer called for the jury to be dismissed.
He said: “Unsurprisingly, Mr Olding has formed the view, as indeed has his legal team, that Ms Long’s intervention is such as to create a substantial risk of prejudice.
“That this cannot be cured. And that, regrettably, this jury shall now have to be stood down and discharged.
“Regrettably, I am compelled to apply to the Court that this jury shall be discharged.”
Meanwhile, prosecutor Toby Hedworth QC described the Twitter furore as a “storm in a teacup”.
He said the defence barrister had chosen his words carefully and expressed confidence the jury would have heeded warnings to steer clear of social media.
After some consideration Judge Patricia Smyth rejected the application.
She said: “This jury has been repeatedly warned from the outset not to look at any press reports. They have also been told not to look at social media and in particular not to look at Twitter.
“It is recognised that jurors are capable of following instructions and I have no reason to think they have not followed every instruction nor do I have any reason to believe they have any knowledge of the tweet.”
Ms Smyth added: “I am not satisfied that there is a real risk of prejudice to this jury and I refuse the application.”
However an official request was made to have the tweet taken down.
Day 40 was to become one of the most dramatic days in courtroom number 12 of the Laganside complex.
A second application to have the jury discharged was made a short time later when Jackson’s defence team raised issues about the judge’s pace, tone and delivery of her legal direction.
Brendan Kelly QC said he made the complaint with a “heavy heart” and “on instruction”.
“I have to make the application,” he said.
Rejecting the criticism, Judge Smyth said she had made changes to the wording of her direction at the request of legal teams and was being “scrupulously careful” to make the case.
She said: “I am studiously anxious to ensure that the points are made.”
Two other men were also acquitted of lesser charges connected to the alleged incident in June 2016.
Blane McIlroy, 26, was found not guilty of exposure while Rory Harrison, 25, was acquitted of perverting the course of justice and withholding information.
Several media outlets took legal action to overturn reporting restrictions which prevented the publication of legal argument made in the absence of the jury.
Restrictions usually fall away when a case concludes because a jury can no longer be prejudiced.
The high-profile trial generated an unprecedented level of public attention.
In a statement outside the court, Jackson’s defence solicitor Joe McVeigh called for a crackdown on social media comment during criminal proceedings.
He said several days had been lost due to problems thrown up by the “intrusive infection of the process” by social media.
The case has also renewed the debate on whether defendants in rape trials should also be entitled to anonymity, with their names only being revealed if they are convicted.
A spokesperson for Alliance said: “We are always conscious of our responsibilities when making any comment related to live court proceedings and exercise great care to avoid any remarks which could be construed as prejudicial.
“The tweets related to a comment from a counsel’s closing address regarding class and not evidence before the court, so were entirely unrelated to and made no reference or inference whatsoever to the guilt or innocence of those on trial.
“Legal contentions alleging prejudice in the context of various remarks on social media were put before the trial judge and after careful consideration she rejected those arguments, a view reinforced by the Attorney General.”