The UK Supreme Court is set to make an official ruling on the definition of a "woman," which has been at the center of a lengthy legal battle between the Scottish government and a women's rights advocacy group. On Tuesday, five judges on Britain's highest court, led by Lord Reeves, began hearing oral arguments concerning the legality of the Scottish Government's guidance regarding the definition of the term "woman" in the Equality Act. The case aims to establish whether a transgender individual who has a gender recognition certificate that identifies them as female can be considered a woman under equality laws.

In 2018, the Scottish Parliament passed legislation requiring 50 percent female representation on the boards of Scottish public bodies. That statute included trans-identified biological men in its definition of women. For Women Scotland (FWS), a women's rights advocacy group, successfully challenged the law, arguing that parliament does not have the authority to change the definition of "woman."

Subsequently, Scottish officials issued guidance stating that a trans-identified biological male who has a gender recognition certificate can be defined as a "woman." FWS is attempting to overturn that decision, believing that the ultimate verdict could have ramifications for sex-based rights as well as single-sex services such as women-only restrooms and facilities.

Trina Budge, director of FWS, told reporters, according to the AP: "Not tying the definition of sex to its ordinary meaning means that public boards could conceivably comprise of 50 percent men, and 50 percent men with certificates, yet still lawfully meet the targets for female representation." The group was granted permission to present its case to the Supreme Court last year after it was rejected by a lower court in 2022.

Aidan O'Neill, a lawyer for FWS, told the high court judges on Tuesday that "sex" should refer to biological sex under the Equality Act. "Our position is your sex, whether you are a man or a woman or a girl or a boy is determined from conception in utero, even before one's birth, by one's body," he said. "It is an expression of one's bodily reality. It is an immutable biological state."
 

Amnesty International, a left-wing human rights group, submitted a written intervention to the court and argued that barring trans-identifying people who hold a gender recognition certificate violates basic human rights. "A blanket policy of barring trans women from single-sex services is not a proportionate means to achieve a legitimate aim," the group said.

Oral arguments in the case will continue on Wednesday.