An aggrieved transgender woman has reported J.K. Rowling, the “Harry Potter” creator, for “commiting a crime” with her statements critical of transgenderism.

India Willoughby, a transgender activist, reported Ms. Rowling to the Northumbria Constabulary in Northern England, claiming that Ms. Rowling had called her a man.

“J.K. Rowling has definitely committed a crime,” Ms. Willoughby told a journalist, Caolan Robertson, on the British network Byline TV. “I’m legally a woman. She knows I’m a woman, and she calls me a man,” the activist, who is the United Kingdom’s first transgender national news anchor, said.

“It’s a protected characteristic,” Ms. Willoughby added, comparing Ms. Rowling’s statements critical of transgender identity to “a hate crime” that “should be treated just as somebody calling a black person the N-word or an Asian person the P-word.”

In the interview, Ms. Willougby added that she had “contacted Northumbria Constabulary.” The Northumbria police have not responded to requests for comments from British outlets. 

The legal bearing of Ms. Willoughby’s report, though, is more complicated. Under Britain’s 2010 Equality Act, discrimination based on protected characteristics, which are said to include gender reassignment, is forbidden.

Yet a British Employment Appeal Tribunal in 2021 established that views critical of transgenderism, such as those espoused by Ms. Rowling, are also listed under the Equality Act as a “protected philosophical belief.”

Over the weekend, Ms. Willoughby’s longstanding conflict with the renowned children’s book author seemingly reached a fever pitch on X, formerly Twitter. On Sunday, a user asked Ms. Rowling if she thought “this lady should use the men’s locker room,” alongside a video of Ms. Willoughby dancing suggestively. 

The “Harry Potter” author responded, retorting, “You’ve sent me the wrong video. There isn’t a lady in this one, just a man reveling in his misogynistic performance of what he thinks ‘woman’ means: narcissistic, shallow and exhibitionist.”

In response to Ms. Willoughby’s statements, Ms. Rowling unrepentantly doubled down. She noted in several concurrent posts on X, “Some time ago, lawyers advised me that not only did I have a clearly winnable case against India Willoughby for defamation, but that India’s obsessive targeting of me over the past few years may meet the legal threshold for harassment.”

“Surprisingly for such an eminent legal authority, he appears to have forgotten that the Forstater ruling established that gender-critical views can be protected in law as a philosophical belief. No law compels anyone to pretend to believe that India is a woman,” Ms. Rowling added. 

The author also noted, “Aware as I am that it’s an offense to lie to law enforcement, I’ll simply have to explain to the police that, in my view, India is a classic example of the male narcissist who lives in a state of perpetual rage that he can’t compel women to take him at his own valuation.”