In the piece, she criticises Sir Keir, as well as shadow home secretary Yvette Cooper, shadow equalities secretary Anneliese Dodds, shadow foreign secretary David Lammy and shadow attorney general Emily Thornberry.
Rowling has been outspoken in her belief that biological women should be able to have separate spaces, and trans women – who were born male – should not be allowed access.
She has been criticised for her position, being widely condemned in recent years for her views on transgender rights, for example claiming that she would rather go to jail than refer to a trans person by their preferred pronouns.
She added: “Grotesque transphobia, which is upsetting. I am every bit as much a woman as JK Rowling.”
Daniel Radcliffe, who became a worldwide star after playing schoolboy wizard Harry in the blockbuster adaptations of the novels, has also criticised her views, and said in an interview last month that the fallout with Rowling “makes me really sad“.
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Image: JK Rowling and India Willoughby. Pic: Reuters/PA
Image: JK Rowling and Daniel Radcliffe at the UK premiere of Harry Potter And The Prisoner of Azkaban in 2004. Pic: PA
Sir Keir was asked about this statement in a recent leaders debate, at which point he said he agreed with Sir Tony Blair that women have vaginas and men have penises.
Rowling says she felt the Labour leader gave “the impression that until Tony Blair sat him down for a chat, he’d never understood how he and his wife had come to produce children”.
She added that she “really wanted to give him the benefit of the doubt”.
In her article, Rowling claims to “have been a Labour voter, a member (no longer), donor (not recently) and campaigner (ditto) all my adult life” – and she wants to see the end of the Conservative government.
According to Electoral Commission records, she gave £1m to the party in 2008, and £8,000 in 2015.
In the article, the author highlighted Ms Dodds for saying what a woman is “depends on what the context is”.
Ms Cooper is criticised for saying she was “not going to get into rabbit holes on this”.
Rowling points to Ms Thornberry for saying: “some women will have penises. Frankly, I’m not looking up their skirts, I don’t care”.
And Mr Lammy draws ire for saying women like Rowling are “dinosaurs hoarding rights”.
Image: David Lammy is among those who Rowling criticised
The Harry Potter author also claims Mr Lammy said that a cervix is “something you can have following various procedures and hormone treatments”.
Rowling wrote: “It’s very hard not to suspect that some of these men don’t know what a cervix is, but consider it too unimportant to Google.”
The NHS definition of the cervix is the opening between the vagina and the womb.
Rowling says the debate for “left-leaning” women like herself “isn’t, and never has been, about trans people enjoying the rights of every other citizen, and being free to present and identify however they wish”.
Instead, she says it is “about the right of women and girls to assert their boundaries”.
She adds: “It’s about freedom of speech and observable truth.
“It’s about waiting, with dwindling hope, for the left to wake up to the fact that its lazy embrace of a quasi-religious ideology is having calamitous consequences.”
The author says she met a mother of a girl with learning difficulties who was “smeared as a bigot and a transphobe for wanting female-only intimate care” for her.
“I cannot vote for any politician who takes issue with that mother’s words,” Rowling adds.
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She concludes: “An independent candidate is standing in my constituency who’s campaigning to clarify the Equality Act.
“Perhaps that’s where my X will have to go on 4 July.
“As long as Labour remains dismissive and often offensive towards women fighting to retain the rights their foremothers thought were won for all time, I’ll struggle to support them.
“The women who wouldn’t wheesht didn’t leave Labour. Labour abandoned them.”
Earlier in the day, Sir Keir ruled out lifting the block on the Scottish government’s controversial gender reforms.
Sky News has approached the Labour Party for comment.
Ms Sultana also said she was “resigning” from the Labour Party after 14 years.
She was suspended as a Labour MP shortly after they came to power last summer for voting against the government maintaining the two-child benefit cap.
Several others from the left of the party, including Mr Corbyn, were also suspended for voting against the government, and also remained as independent MPs.
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However, Ms Sultana was still a member of the Labour Party – until now.
Mr Corbyn has previously said the independent MPs who were suspended from Labour would “come together” to provide an “alternative.
The other four are: Iqbal Mohamed, Shockat Adam, Ayoub Khan and Adnan Hussain.
Mr Corbyn and the other four independents have not said if they are part of the new party Ms Sultana announced.
In her announcement, Ms Sultana said she would vote to abolish the two-child benefit cap again and also voted against scrapping the winter fuel payment for most pensioners.
Ms Sultana also voted against the government’s welfare bill this week, which was heavily watered down as Sir Keir Starmer tried to prevent a major rebellion from his own MPs.
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Protesters block Israeli arms manufacturer in Bristol
On Wednesday, Ms Sultana spoke passionately against Palestine Action being proscribed as a terror organisation – but MPs eventually voted for it to be.
She said to proscribe it is “a deliberate distortion of the law to chill dissent, criminalise solidarity and suppress the truth”.
Ms Sultana said they were founding the new party because “Westminster is broken but the real crisis is deeper – just 50 families now own more wealth than half the UK population”.
She called Reform leader Nigel Farage “a billionaire-backed grifter” leading the polls “because Labour has completely failed to improve people’s lives.
Image: Ms Sultana called Nigel Farage a ‘billionaire-backed grifter’. Pic: PA
The MP, who has spoken passionately about Gaza, added: “Across the political establishment, from Farage to Starmer, they smear people of conscience trying to stop a genocide in Gaza as terrorists.
“But the truth is clear: this government is an active participant in genocide. And the British people oppose it.
“We are not going to take this anymore.”
A Labour Party spokesperson said: “In just 12 months, this Labour government has boosted wages, delivered an extra four million NHS appointments, opened 750 free breakfast clubs, secured three trade deals and four interest rate cuts lowering mortgage payments for millions.
“Only Labour can deliver the change needed to renew Britain.”