A former aide to Jeremy Corbyn has told a High Court judge she was “horrified” when television presenter Rachel Riley posted a tweet two years ago which appeared to be “endorsing” an attack on the then Labour leader.

Laura Murray, who had responded with a tweet describing Ms Riley as “dangerous” and “stupid”, told Mr Justice Nicklin she had been “shocked and outraged”.

She said she thought Ms Riley’s tweet was “reckless and irresponsible”.

Ms Riley, 35, a numbers expert on the Channel 4 show Countdown, posted a tweet in March 2019 after Mr Corbyn had been hit with an egg while visiting a mosque.

Ms Murray, 32, responded a few hours later, and said nobody should “engage” with Ms Riley.

Ms Riley has sued Ms Murray for libel, saying the “dangerous” and “stupid” tweet caused “serious harm” to her reputation.

The judge has heard that Ms Riley initially posted a screenshot of a January 2019 tweet by Guardian columnist Owen Jones, about an attack on former British National Party leader Nick Griffin, which 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 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 says she was being sarcastic in her tweet and did not call Mr Corbyn a Nazi.

Ms Murray was “stakeholder manager” in Mr Corbyn’s office and went on to be the Labour Party’s head of complaints.

In her defence to Ms Riley’s libel claim, she says what she tweeted was true, and reflected her honestly held opinions.

Mr Justice Nicklin is overseeing a trial at the High Court in London, which began on Monday and is due to end on Wednesday.

Ms Murray, who is now a trainee teacher, told Mr Justice Nicklin on Tuesday that she had thought Ms Riley’s tweet was “misjudged and stupid”.

“I was horrified by what the claimant had said, which I thought was reckless and irresponsible given all that had happened and also given the claimant’s high profile and influence,” she said in a written witness statement.

“My reading of the claimant’s original tweet was that she was taking Owen Jones’ advice – that Nazis deserve to have eggs thrown at them – and applying it to the assault which had just taken place on Mr Corbyn.

“By adding the words ‘good advice’, the claimant appeared to me to clearly be endorsing and encouraging the act.

“I felt strongly that the claimant’s tweet sent a dangerous message to the wider world and was a misjudged and stupid thing to do.”

Ms Murray said a man had attacked Mr Corbyn by “striking him on the head whilst holding an egg”.

She told the judge: “I was just shocked and outraged by her tweet.”

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

He concluded that the tweet meant Ms Riley had “publicly stated” 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”.

He has now been asked to consider whether serious harm was caused to Ms Riley’s reputation, and whether Ms Murray had a defence of truth, honest opinion or public interest.

Ms Riley, who studied mathematics at Oxford University, has told the judge she is Jewish and has a “hatred of anti-Semitism”.

She said she spoke out against anti-Semitism and thought the Corbyn-led Labour Party was “fostering anti-Semitism”.

Ms Riley has told the trial she had been criticised by other Twitter users after posting the “good advice” tweet before Ms Murray joined the discussion.

She said she believed Ms Murray was blowing a “dog whistle”.

Ms Murray said her stakeholder manager’s job had involved her working with the Jewish community.

“Due to the significant problems between the Labour Party and the Jewish community, and the increasing prevalence of anti-Semitic incidents within the Labour Party, liaison and work with Jewish stakeholders was a large part of my role,” she told Mr Justice Nicklin.

“I met regularly with Jewish stakeholders and I worked closely with them to try to find solutions to the problem of anti-Semitism which was becoming evident within parts of the Labour Party membership.”