Mr Justice Robert Jay QC was leading counsel to the Leveson Inquiry into the culture, practices and ethics of the press from 2011 to 2012, and was appointed a High Court judge in June 2013.
Following a week-long trial in London in 2017, Mr Justice Jay dismissed a claim for damages brought by 67-year-old businessman Jan Tomasz Serafin, who complained about an article in a Polish language magazine.
But his decision was overturned on Friday by three Court of Appeal judges, who said Mr Justice Jay’s interventions during Mr Serafin’s evidence were “highly unusual and troubling”.
Lords Justice Lewison, McCombe and Haddon-Cave said in a ruling that the judge had acted in a “manifestly unfair and hostile” way towards the claimant, who was not represented by lawyers during the hearing.
The judges said: “On numerous occasions, the judge appears not only to have descended to the arena, cast off the mantle of impartiality and taken up the cudgels of cross-examination, but also to have used language which was threatening, overbearing and, frankly, bullying.
“One is left with the regrettable impression of a judge who, if not partisan, developed an animus towards the claimant.”
They said the judge’s conduct towards Mr Serafin, a Polish national who has lived in London since the 1980s, was “all the more surprising and troubling” given that he was acting as a litigant in person and English was not his first language.
The judges added: “In our view, the judge not only seriously transgressed the core principle that a judge remains neutral during the evidence, but he also acted in a manner that was manifestly unfair and hostile to the claimant.
“Not all departures from good practice render a trial unfair … nevertheless, we have carefully considered and reflected upon this matter and are driven to the conclusion that the nature, tenor and frequency of the judge’s interventions were such as to render this libel trial unfair.”
In appeal documents, Mr Serafin’s lawyers said that at one point during the trial Mr Justice Jay had “threatened the claimant with prosecution and imprisonment for forgery”.
His barrister, Alexandra Marzec, also said the judge “appeared to regard hearing from the claimant in any capacity as a waste of time”.
She said that, halfway through the trial in response to defence lawyers, the judge had said: “I would not even bother … I think we have got to assume every point is lies.”
Ms Marzec added: “It was to the claimant’s credit that he managed to continue to present his case in the face of this show of contempt for him by the bench.”
Mr Leech said: “Robert Jay should resign following the trenchant and frankly unheard of criticism of the Appeal Court.
“He has obviously failed to make the essential transition from partisan QC – which he was exceptionally good at – to impartial High Court Judge which he is clearly appalling at; this is real life, with real people and real consequences – not an episode of Judge John Deed.”