JK Rowling has clashed with a trans activist and urged Sir Keir Starmer to break his silence after the Supreme Court ruled a woman is someone born biologically female. The author said many women are waiting to hear the Prime Minister’s views on the legal ruling. In a post on X, Ms Rowling, added: “After all, he’s the man who decreed: ‘A woman is a female adult, and in addition to that trans women are women, and that is not just my view, that is actually the law’.”

Ms Rowling accused Sir Keir, then Leader of the Opposition, of misrepresenting equalities law when he first made the remarks in March 2022. She tweeted at the time that the comments were “yet another” sign Labour couldn’t be counted on to defend women’s rights. In 2023, Sir Keir pledged to support trans rights, but not at the expense of women’s rights. He said 99.9% or women don’t have a penis, adding a small number of people identify themselves under a gender different than the one they were born as. The Harry Potter author renewed her criticism hours after the Supreme Court ruled the terms “woman” and “sex” in the Equality Act refer to a biological woman and biological sex.

In their judgment, Lord Hodge, Lady Rose and Lady Simler said while the word “biological” does not appear in the definition of man or woman in the Equality Act, “the ordinary meaning of those plain and unambiguous words corresponds with the biological characteristics that make an individual a man or a woman”.

The justices said that transgender people are still protected from discrimination, but that “gender reassignment and sex are separate bases for discrimination and inequality”.

Campaign group For Women Scotland (FWS) brought a series of challenges over the definition of “woman” in Scottish legislation mandating 50% female representation on public boards.

The dispute centred on whether someone with a gender recognition certificate (GRC), recognising their gender as female, should be treated as a woman under the UK 2010 Equality Act.

Out of some 66 million people in England, Scotland and Wales, about 116,000 identified as trans in the latest census count. About 8,500 GRCs have been issued.

The ruling was lauded by gender critics as a victory despite the judges’ warning it shouldn’t be seen as a “triumph” of one side over another.

Ms Rowling was among the gender critics celebrating the Supreme Court ruling. On Thursday, she continued to hit out at Sir Keir and lashed out at trans activist Dr Helen Webberley.

Dr Webberley had told gender critics to “GET A LIFE” if they felt their “precious space” could be invaded by “those terrifying creatures with… a PENIS”. A fellow X-user shot back sarcastically, “[w]e’ll let our girls be raped to prove you right”.

To which Dr Webberley replied: “We must not teach our young girls and women that all that someone who has a penis wants to do is rape them. It’s just totally and utterly the wrong message. Penises are there for us to enjoy, not fear!”

Ms Rowling seized on the post, sharing it with her 14.3 million followers and commenting: “Yes, what better message to teach a young girl that if a strange man gets out his dick in front of her, she shouldn’t be afraid, but enjoy it.

“Helen Webberley is a pro-puberty blocker doctor who runs an online gender clinic.”

It wasn’t the first disagreement between the pair, with Dr Webberley retweeting an article in which it was revealed a school had dropped JK Rowling and Winston Churchill as house names.

Since the landmark Supreme Court ruling, the head of the Equality and Human Rights Commission, Kishwer Falkner, has said trans women will be excluded from women’s toilets, hospital wards and sports teams.

Baroness Falkner said the “enormously consequential” ruling brought clarity and would prompt her organisation to update public codes by the summer to comply.

She told the BBC: “Single-sex services like changing rooms must be based on biological sex. If a male person is allowed to use a women-only service or facility, it isn’t any longer single-sex, then it becomes a mixed-sex space.”

British Transport Police said a day after the judgment that it had adopted a new “interim position” which will see trans people held in custody strip searched by an officer in line with their birth sex.

It means trans women in custody will be searched by male officers, while officers who are trans women will no longer be able to search female detainees. The force stressed someone can object and ask to be searched by another officer.

Sarah Savage, a trans woman who is the chief executive and co-founder of Trans Pride Brighton, described the ruling as “extremely worrying”.

One domestic abuse charity, Refuge, said the court ruling “will not change” the way it operates as it remains “firmly committed to supporting all survivors of domestic abuse, including trans women”.

A director of community group TransActual, jane fae – who spells her name in lower case letters – also expressed concern.

The 67-year-old from Letchworth said: “As I get older I may need hospital care, I foresee being forced into the indignity of being on a male ward, that would be upsetting to say the least.”