The argument began on Sunday, when the author dismissed a video of Willoughby as “a man revelling in his misogynistic performance of what he thinks ‘woman’ means: narcissistic, shallow and exhibitionist”.

JK Rowling has been labelled a “transphobe” for her “grotesque” views on trans rights after she deliberately misgendered Britain’s first transgender newsreader, India Willoughby.

The Harry Potter author has been widely condemned in recent years for her views on transgender rights, having claimed that she would rather go to jail than refer to a trans person by their preferred pronouns.

On Sunday, Rowling posted several comments on X complaining about trans women being allowed in female locker rooms.

When another X user sent her a video of Willoughby, asking if she thought “this lady should use the men’s locker room?”, Rowling replied: “You’ve sent me the wrong video. There isn’t a lady in this one, just a man revelling in his misogynistic performance of what he thinks ‘woman’ means: narcissistic, shallow and exhibitionist.”

The user then asked: “If India Willoughby is a ‘misogynist’ why did she become a woman? Think.”

Rowling wrote back: “India didn’t become a woman. India is cosplaying a misogynistic male fantasy of what a woman is.”

Willoughby is Britain’s first transgender newsreader and the first transgender co-host of an all-women talk show, ITV’s Loose Women.

On Monday, she posted on X that she was “genuinely disgusted by this [JK Rowling’s comments]. Grotesque transphobia, which is upsetting. I am every bit as much a woman as JK Rowling.

“Recognised in law, and by everyone I interact with every day. The debate about whether JK Rowling is a transphobe is over.”

In a separate tweet, Rowling added: “Accurately sexing trans-identified men who send misogynistic abuse to women is not discrimination. ‘Man’ is not a slur… there is no human right to universal validation.”

Willoughby went further later, accusing Rowling of “indisputable transphobic bullying” and asking: “If I ever get murdered, you know who to blame. #StochasticTerrorism.”

Stochastic terrorism refers to when popular figures publicly demonise a person or group in such a way that inspires their supporters to commit a violent act against the target of the speech.

The pair also clashed in January last year, when Willoughby posted on X she was “more of a woman than JK Rowling will ever be”.

The author replied, saying “citation needed”.

Last week, Rowling hit out at Sky News for referring to murderer Scarlet Blake as a woman in its reporting.

Blake was jailed for life after being convicted of the murder of Jorge Martin Carreno as part of a sexual fantasy inspired by a Netflix documentary.

After it emerged that the killer had transitioned to female, Rowling criticised Sky News for referring to her as a woman on X.

During the trial, Blake was referred to by the court using female pronouns. At the trial’s conclusion, the Ministry of Justice confirmed Blake was being held at a male prison.