Television presenter Rachel Riley’s reputation was damaged when she was criticised in a tweet posted by a former senior aide to ex-Labour leader Jeremy Corbyn, a lawyer has told a High Court judge overseeing a libel trial.

William Bennett QC told Mr Justice Nicklin on Monday that the tweet posted by Laura Murray about two years ago caused serious harm to Ms Riley 35, who appears in the Channel 4 show Countdown.

Ms Murray is disputing the claim.

Mr Justice Nicklin began overseeing the trial, at the High Court in London, on Monday.

The trial is due to end late this week.

Ms Murray had posted the tweet on March 3 2019, after an egg was thrown at Mr Corbyn, who was then the Labour leader, by a Brexit supporter when he was visiting Finsbury Park Mosque, in north London.

She had been responding to a tweet posted by Ms Riley, Mr Justice Nicklin was told.

Ms Riley had initially retweeted a January 2019 tweet by Guardian columnist Owen Jones, about an attack on former British National Party leader Nick Griffin, in which Mr Jones had said: “I think sound life advice is, if you don’t want eggs thrown at you, don’t be a Nazi.”

She had added “Good advice”, with emojis of a red rose and an egg.

Later, Ms Murray had tweeted: “Today Jeremy Corbyn went to his local mosque for Visit My Mosque Day, and was attacked by a Brexiteer.

“Rachel Riley tweets that Corbyn deserves to be violently attacked because he is a Nazi.

“This woman is as dangerous as she is stupid. Nobody should engage with her. Ever.”

Ms Riley has sued Ms Murray for libel.

She says the tweet contained “defamatory statements of fact” about her.

“We do say that the tweet complained of did cause serious harm,” Mr Bennett told the judge.

“She was accused of risking inciting violence and told she was dangerous.”

He said the tweet had been published to a “huge number of people”.

A barrister representing Ms Murray disagreed with the case put forward by Ms Riley.

William McCormick QC told the judge, in a written case outline, that Ms Murray’s tweet was “true”.

“The claimant (Ms Riley) chose to tweet to her 625,000-plus followers about a violent attack in a manner which was both stupid and dangerous,” he said.

“It was obvious that her tweet would provoke hostile reactions of the kind that did in fact emerge.

“What the defendant (Ms Murray) tweeted was true, reflected her honestly-held opinions and was a responsible exercise of her own rights of expression on a matter of real public importance.”

He said it was “tolerably clear” that Ms Riley had “wrongly regarded” the libel claim as part of a long-running dispute over anti-Semitism in the Labour Party.

Mr McCormick said it was an issue on which she “feels strongly”.

But he said the case was not about anti-Semitism but about the “need for restraint in public discourse”.

Mr Justice Nicklin had ruled at an earlier hearing that Ms Murray’s tweet was defamatory.

The judge had concluded that the tweet meant that: Ms Riley had “publicly stated” that Mr Corbyn had been attacked when visiting a mosque; that he “deserved to be violently attacked”; by doing so, she had shown herself to be a “dangerous and stupid person” who “risked inciting unlawful violence”; and, that people should not “engage with her”.

Mr Bennett said “relevant issues” at the trial were: whether serious harm had been caused to Ms Riley’s reputation, and, whether Ms Murray had a “truth” defence, an “honest opinion” defence, or a “public interest” defence.

Ms Riley told the judge that she was being “sarcastic” in her tweet.

“I wasn’t directing it at Owen Jones,” she said.

“I was directing it at the left.”

She said Ms Murray “must have known” that “I didn’t say those words”.

Ms Riley was questioned by Mr McCormick.

He suggested that Ms Riley’s tweet had generated a Twitter debate around whether or not she had called Mr Corbyn a Nazi.

Ms Riley accepted that she regarded Mr Corbyn as “anti-Semitic”.

But she said she had not called Mr Corbyn a Nazi and added: “I didn’t use the word Nazi.”

The judge heard that Ms Riley was a “prominent and regular” critic of the Labour Party.