Former Labour leader Jeremy Corbyn is trying to overturn a High Court judge’s ruling after being sued for defamation by a political blogger.
Mr Corbyn has mounted an appeal against preliminary findings made by Mr Justice Saini.
Three appeal judges are considering arguments at a Court of Appeal hearing in London on Tuesday.
Lawyers representing Mr Corbyn said the case involved political and free speech and needed “close scrutiny”.
Richard Millett has complained about things Mr Corbyn said in a BBC television interview with broadcaster Andrew Marr in September 2018.
He says Mr Corbyn defamed him by accusing him of being “disruptive and abusive” at a 2013 meeting featuring a Palestinian speaker.
Mr Corbyn disputes Mr Millett’s claims and denies defaming him.
Mr Justice Saini made preliminary decisions about the meaning of words Mr Corbyn used – and about whether he was stating facts or expressing opinion – in July following a High Court hearing.
The judge concluded that Mr Corbyn was making “factual” allegations “as to Mr Millett’s behaviour”.
Lawyers representing Mr Millett argued that to accuse someone of being “disruptive and abusive to the degree in issue” must have “caused him to have been defamed”.
Lawyers representing Mr Corbyn disagreed and argued what had been said did not lower Mr Millett in the “estimation of right-thinking people”.
Mr Justice Saini concluded that the “words complained of” referred to Mr Millett and “bore a meaning defamatory of Mr Millett”.
He said what had been stated suggested “conduct falling below the standards expected of citizens in modern British society”.
Mr Corbyn wants appeal judges to overturn decisions made by Mr Justice Saini.
On Tuesday, Anthony Hudson QC, who is representing Mr Corbyn, told Sir Geoffrey Vos, the Master of the Rolls, Dame Victoria Sharp, president of the Queen’s Bench Division of the High Court, and Lord Justice Warby, that the case involved political and free speech, and required close scrutiny.
He suggested that Mr Justice Saini’s ruling could have a “chilling” effect on political speech.
Judges have heard that, shortly after the meeting involving the Palestinian speaker, Mr Corbyn, who had not yet become the Labour leader, had addressed a conference organised by the Palestinian Return Centre.
Mr Corbyn had said “the Zionists” who had attended the meeting had “berated” the Palestinian speaker.
He had said these “Zionists” did not want to study history and did not understand English irony.
In August 2018, when Mr Corbyn had become leader of the Labour Party, a video of that “irony speech” was made public.
Lawyers representing Mr Millett said there had subsequently been “huge publicity” about “the fact that” Mr Corbyn’s statements during the irony speech had been directed at Mr Millett.
Mr Marr had then asked Mr Corbyn about the “irony speech”, during an interview on The Andrew Marr Show, in September 2018.
Judges have heard how Mr Corbyn had told Mr Marr that he had not been “anti-Semitic”.
He said two people had been “incredibly disruptive”, and he had accused them of not understanding English irony, because he wanted to defend the Palestinian speaker.
Mr Millett says people who had read media articles saying statements Mr Corbyn made during the “irony speech” were directed at him, and would have realised that the Labour leader was referring to him when telling Mr Marr about “two people” who had been “incredibly disruptive”.