UK Supreme Court Ruling: A Victory for Biological Sex

The UK Supreme Court has just delivered a landmark ruling that represents a decisive victory for common sense, and for those who argue that sex-based rights depend on the freedom to use language accurately. By confirming that the Equality Act 2010 definition of “woman” refers to biological sex rather than acquired gender, the Court has reaffirmed the linguistic foundations on which statutory protections for women rest. In doing so, it has set the UK apart from the direction of travel in much of Europe, where gender identity increasingly overrides biological sex in policy and in law.

The Legal Dispute Over Gender Representation

In a unanimous judgment handed down this week, five justices ruled that the words “woman” and “sex” in the Equality Act refer to biological categories. The decision concludes a lengthy legal dispute between the Scottish Government and the feminist advocacy group For Women Scotland over whether trans women with a Gender Recognition Certificate (GRC) could be counted towards a 50 per cent gender balance target for women on public boards.

Although framed as a question of statutory interpretation rather than social policy, the implications are significant.

The Court made clear that the various public and private bodies who have duties under the Equality Act cannot redefine the legal meaning of “woman” to suit policy objectives. And while Deputy President Lord Hodge cautioned against seeing the ruling as “a triumph of one or more groups in our society at the expense of another”, the fact is that in practical terms, it is just that – a decisive moment for biological women in halting the encroachment of another group into their legal, social and institutional space.

The Court’s decision will influence how single-sex services, equal pay frameworks, and positive action provisions are interpreted and applied across the UK.

At the heart of the case was a now-retracted section of the Gender Representation on Public Boards (Scotland) Act 2018, which included certain trans women – those with the protected characteristic of gender reassignment – within its definition of “woman”. After that provision was found unlawful by the Court of Session in 2022, the Scottish Government issued revised guidance. This new guidance claimed that trans women with a GRC, who under the Gender Recognition Act 2004 (GRA) are deemed to have changed their legal sex “for all purposes”, could still be counted as women under the Equality Act.

The Supreme Court rejected that argument. It held that the Equality Act is a comprehensive statute that treats “sex” and “gender reassignment” as distinct protected characteristics. While section 9(1) of the GRA provides that a person’s acquired gender applies “for all purposes”, the Court concluded that this rule is disapplied where its application would make another law incoherent. Under section 9(3), the meaning of “sex” in the Equality Act must be interpreted in light of the Act’s own structure, language and purpose. That, the Court found, requires a biological reading.

Applying a certificated sex interpretation, it added, would render key provisions of the Equality Act unworkable, including those concerning pregnancy and maternity, equal pay, and the legality of single-sex services. The Court therefore concluded that the terms “woman” and “man” in the Act refer to biological sex.

The UK's Approach vs. European Trends

By reaffirming that “sex” in equality law refers to biology, the UK Supreme Court has placed Britain increasingly at odds with prevailing legal and political trends across Europe. In much of the EU, gender identity is now treated as legally interchangeable with sex, whether through self-identification regimes or the removal of biological sex markers from official documents.

The European Court of Human Rights, for instance, has consistently held that states have a positive obligation to provide quick, transparent, and accessible procedures for changing registered sex markers, viewing failure to do so as a violation of the right to private life under Article 8 of the European Convention on Human Rights. Similarly, the EU’s LGBTIQ Equality Strategy (2020-2025) promotes “accessible legal gender recognition based on self-determination and without age restriction”.

In 2024, the European Court of Justice ruled that member states must recognise legal changes to gender identity processed elsewhere within the EU. The case concerned Arian Mirzarafie-Ahi, a transgender man who sued Romania for refusing to recognise the name and gender identity changes he had initiated in Britain, when it was still a member state. The Court found that Romania violated his rights to citizenship and free movement by refusing to update his Romanian identity documents. “Gender, like a first name, is a fundamental element of personal identity,” the Court said in a news release accompanying its ruling.

National legislatures have followed suit. Germany’s Self-Determination Law (2024) allows individuals aged 14 and older to change their legal gender and first name by simply filing a declaration at the registry office, without medical or judicial requirements. Spain’s Gender Self-Determination Law (2023) permits individuals over 16 to change their legal gender by simple declaration, with provisions for minors as young as 14 under certain conditions.

Poland, too, has eased restrictions. In 2023, its Supreme Court removed the requirement that trans people involve their parents in court proceedings for gender recognition. Other countries, including Finland, Iceland and Ireland, are among some of the other countries to have adopted similar self-ID laws in the past decade, reflecting a broader trend across Europe toward recognising gender identity in law.​

The Wider Relevance of the Judgment

Against this backdrop, the UK’s top court has unequivocally declared that, for the purposes of legal rights and protections, sex means biology, not identity.

In its detailed examination of the Act, the Supreme Court explained that while the terms “man” and “woman” are not defined using the word “biological”, their statutory definitions – “a female/male of any age” – reflect a binary, sex-based understanding. Reinterpreting them to include individuals with acquired legal status, it said, would create legal uncertainty, undermine group-based protections, and make enforcement practically impossible.

The Court’s ruling has been welcomed by women’s rights campaigners as long-overdue, not least because it safeguards the ability of service-providers, employers and public authorities to make lawful distinctions based on sex, without needing access to a person’s confidential GRC status.

Among gender-critical advocates, in particular, the judgment was hailed as a return to legal common sense. JK Rowling said it would protect “the rights of women and girls across the UK”. Kate Barker, chief executive of the LGB Alliance, added that it “confirms that the words ‘gay’ and ‘lesbian’ refer to same-sex sexual orientation and makes it absolutely clear that lesbians wishing to form associations of any size are lawfully entitled to exclude men, whether or not they possess a GRC”.

Former Olympic swimmer Sharron Davies also welcomed the Court’s intervention, noting that “single-sex spaces have become today, clarified in law, as a biological single-sex space,” including “sport, changing rooms, rape crisis centres and prisons.”

The Court, however, was careful to stress that the judgment does not deprive trans people of protection under the Equality Act. Those with or without a GRC remain covered under provisions on gender reassignment, perceived sex and association with a protected group. But what the judgment does do is put an end to a period of ambiguity in public policy and equality law, making clear that the meaning of “woman” cannot be revised through policy guidance or evolving institutional practice. If Parliament wishes to change the legal definition of sex, it must now do so explicitly.

A Narrow Yet Revolutionary Ruling

In one sense, the ruling is narrow, addressing only the interpretation of UK equality law rather than the broader debate over gender ideology. But it also establishes a principle with relevance far beyond Britain: that rights cannot be defended if the words that describe them lose their meaning.

The late American sociologist Harvey Sacks once observed that “what the dominant categories” of everyday life effectively own is “how people perceive reality”, and that there is therefore “an order of revolution which is an attempt to change how it is that persons see reality”. That is what is at stake in the legal redefinition of sex. The UK Supreme Court has drawn a line – a modest, reasoned line, but a ‘revolutionary’ one nonetheless – affirming that in the grand lexicon of legal categories, at least, reality must remain visible. Others in Europe should take note.

Dr. Frederick Attenborough

Dr Frederick Attenborough is the Research Director of the Free Speech Union.

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