In a landmark decision that follows years of confusion, anger, and campaigning, the UK’s highest court has ruled that the words “woman” and “sex” refer to “a biological woman and biological sex.”

The case sought to clarify the question of whether a person who holds an official certificate recognizing that individual’s gender as female is entitled to women’s rights protections under the law.

A commonly cited example was the question of whether women-only services—such as rape crisis support groups—were allowed to exclude men with gender recognition certificates.

A gender recognition certificate indicates that a person’s chosen gender identity is legally recognized.

Obtaining the certificate requires a medical diagnosis of gender dysphoria, having lived as the identified gender for at least two years, and the intention to live as that self-identified gender until death.

This legislation was passed by the Scottish Parliament and mandated that 50 percent of individuals on public boards be female. Its definition of “female” included males who identify as women.

For Women Scotland’s lawyers argued that not tying the definition of sex to its “ordinary meaning” could have far-reaching consequences for sex-based rights, as well as for “everyday single-sex services” such as bathrooms, changing rooms, hospital wards, and domestic violence and rape crisis centers.

Counsel for the Scottish government argued at the Supreme Court hearing in November 2024 that a person with a gender recognition certificate is “recognized in law” as having changed sex.

Delivering the judgment, Lord Patrick Hodge, deputy president of the UK Supreme Court, said the central question is how the words “woman” and “sex” are defined in the Equality Act 2010.

“The terms woman and sex in the Equality Act 2010 refer to a biological woman and biological sex,” Hodge said.

This means that men who identify as women and who hold a gender recognition certificate may be excluded from single-sex spaces if “proportionate.”

The judges said that 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 court said this interpretation of the law does not disadvantage people who identify as transgender, who were described as a “potentially vulnerable group.”

They said the group is still protected from discrimination, and that if needed, they “would be able to invoke the provisions on direct discrimination and harassment, and indirect discrimination.”

The justices also said that transgender-identifying people are protected from discrimination on the grounds of gender reassignment.

It also covers a limited number of criminal cases from Scotland, which technically has a separate legal system.

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However, a Supreme Court judgment in the UK carries a lot less weight than it would in the United States.

Lawmakers in the UK are not bound by a codified constitution that can only be changed through a supermajority and other hurdles to ratification.

Rather, Parliament can effectively negate a Supreme Court ruling by voting in new legislation.

The Equality and Human Rights Commission, which is responsible for the promotion and enforcement of equality and nondiscrimination laws in the UK, is expected to put an updated statutory code of practice before Parliament by summer, and said it is working “at pace to incorporate the implications of [the] judgment” into the code for public bodies setting out their duties under the Equality Act.

This means that males in custody will be searched by male officers, while male officers who identify as trans women will no longer be able to search female detainees.

The National Police Chiefs’ Council has said it will be reviewing its policies, but “will need time to consider the full implications of the court’s decision, as will many other public bodies.”

Baroness Kishwer Falkner, Equality and Human Rights Commission chairwoman, said the ruling by the court was “enormously consequential,” and that she will pursue organizations that fail to update their policies.

“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.”

When asked if it is now the case that males cannot take part in women’s sports, Falkner said, “Yes, it is.”

However, Lord Jonathan Sumption, former Supreme Court justice, told the BBC that while the ruling means that organizations are allowed to exclude males from women-only facilities, they may not be obliged to do so.

The lawyer and historian said that in sports, for example, it would be down to individual governing bodies to decide who is allowed to compete in women’s sports.

“They could decide to allow trans women to compete on the same basis as biological women,” he said. “Some sporting authorities do, although I think that in light of the latest judgment, they would be wise to say so expressly in their rules.”

Women and Equalities Minister Bridget Phillipson has said that men who identify as trans women should use male toilets, but suggested that businesses should ensure that “they have appropriate provision in place,” which could mean unisex facilities.

She told BBC Radio 4 on April 22 that the Supreme Court ruling made it clear that “services should be accessed on the basis of biological sex.”

In March 2022, while still in opposition, Starmer said, “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.”

When asked on April 22 to repeat his previous statement that “trans women are women,” he said, “I think the Supreme Court has answered that question.”

“Saying ‘trans women are women’ was never true in fact, and now isn’t true in law either,” she wrote on social media platform X on April 16.

“This is a victory for all of the women who faced personal abuse or lost their jobs for stating the obvious. Women are women and men are men: you cannot change your biological sex.”

Scottish First Minister John Swinney said the government in Edinburgh accepts the ruling, noting that “protecting the rights of all” will inform its response.

“It took three extraordinary, tenacious Scottish women with an army behind them to get this case heard by the Supreme Court,” Rowling wrote. “I’m so proud to know you.”

The LGB Alliance, a charity founded to support the rights of same-sex attracted people concerned about the promotion of gender identity ideology, and which provided a written submission in the case, said it is “delighted” with the “momentous” ruling.

The group said the decision has “potentially concerning consequences for trans people,” but that it is “important to stress that the court has been clear that trans people are protected under the Equality Act against discrimination and harassment.”