“Interpreting sex as certificated sex would cut across the definitions of man and woman in the EA and thus the protected characteristic of sex in an incoherent way,” Lord Patrick Hodge, deputy president of the court, said following the ruling. “It would create heterogeneous groupings.”

He continued, “As a matter of ordinary language, the provisions relating to sex discrimination, and especially those relating to pregnancy and maternity and to protection from risks specifically affecting women, can only be interpreted as referring to biological sex.”

For Women Scotland, a women’s rights organization that opposes self-designation of gender identity, brought the case to court after the Scottish government expanded its definition of “women” to include transgender-identifying people.

The organization opposed the move on the grounds that it allowed biological men who self-identify as women to use biological women-only spaces such as bathrooms, changing rooms, hostels, and gender-segregated prisons and granted them access to charities and other resources meant to aid biological women specifically.

The court counseled against interpreting the judgment as a “triumph for one or more groups in our society at the expense of another,” — emphasizing that transgender-identifying people remain a protected class “on the grounds of gender reassignment.” They are also still capable of invoking protections against discrimination or harassment on the basis of their gender identity separate from self-identification as a woman.

The ruling was a relief for Prime Minister Keir Starmer, as some people expected the court to reject the case and force the U.K. government to handle the matter.

A spokesperson for the government welcomed the “clarity and confidence” brought by the decision.

“We have always supported the protection of single-sex spaces based on biological sex,” the spokesperson said, according to the Guardian. “Single-sex spaces are protected in law and will always be protected by this government.”

For Women Scotland welcomed the decision as a major victory in its cause, with supporters celebrating outside the court after the ruling was announced.

“The decision by the U.K.’s highest court provides definitive protection to women and girls, gives clarity to organizations, and clears up the confusion created by the Scottish Government in earlier rounds of this case,” the group said in a statement.

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“Nonetheless, policies based on self-identification remain in place across the U.K., in hospitals, police forces, schools and prisons,” the statement continued. “The U.K. and devolved governments and the Equality and Human Rights Commission need to take responsibility for their role in this, take urgent steps to clear up the confusion, and ensure the ruling has effect on the ground.”

The Scottish government acknowledged and accepted the court’s ruling and promised to align its policies with the new guidance.