“Sex” Means Biological Sex, Supreme Court Confirms in Landmark Equality Act Ruling

Few questions in contemporary equality law have generated as much doctrinal uncertainty — or as intense scrutiny — as the definition of “sex” under the Equality Act 2010. Against a backdrop of evolving societal understandings of gender, the task of statutory interpretation has grown increasingly complex. In For Women Scotland Ltd v The Scottish Ministers [2024] UKSC 31, the Supreme Court has now provided a judgment of both constitutional and practical significance. In unequivocal terms, the Court held that “sex”, as a protected characteristic under the Act, refers to biological sex — not to gender identity, nor to the acquired gender recognised by a Gender Recognition Certificate.

While the decision comes at a time of heightened sensitivity around gender and inclusion, its primary contribution is doctrinal: it reaffirms the settled meaning of legislative language and clarifies the respective functions of the Equality Act 2010 and the Gender Recognition Act 2004. The judgment does not seek to resolve matters of policy or belief. Rather, it restores legal certainty to the operation of a statute intended to provide structured protection across nine protected characteristics.

Background to the Appeal

The appeal concerned statutory guidance issued under the Gender Representation on Public Boards (Scotland) Act 2018, which had expanded the category of “woman” to include individuals who, although biologically male, had either acquired a GRC recognising them as female or were in the process of gender reassignment. For Women Scotland Ltd challenged the legality of this definition, contending that it conflicted with the meaning of “woman” under the Equality Act 2010, which — they argued — refers to biological sex.

Although the Inner House of the Court of Session upheld the statutory guidance, the Supreme Court disagreed. It concluded that the Scottish Ministers lacked legislative competence to redefine terms already governed by the Equality Act — a reserved matter under the Scotland Act 1998. Further, the Court held that the Equality Act does not permit such a redefinition.

Ratio of the Judgment

The Supreme Court’s reasoning proceeds from a close reading of the statutory scheme. The judgment underscores that the Equality Act treats sex and gender reassignment as distinct and independent protected characteristics. It observes that key provisions — including those relating to single-sex services (Schedule 3), occupational requirements (Schedule 9), and positive action (Sections 158–159) — presuppose a consistent and biologically grounded definition of sex.

The Court found no textual basis for the view that the acquisition of a GRC alters a person’s sex for the purposes of these provisions. While the Gender Recognition Act 2004 facilitates certain legal recognitions following gender transition, it does not amend the meaning of “sex” under the 2010 Act. To interpret otherwise, the Court reasoned, would risk creating internal incoherence within a statutory regime that carefully balances multiple protected characteristics.

Practical Legal Consequences

The implications of the judgment are wide-ranging, particularly in areas where the law expressly permits or requires distinctions on the basis of sex. As a matter of legal necessity, the following consequences now flow:

• Positive Action: Initiatives aimed at addressing disadvantage or under-representation on grounds of sex must be directed towards individuals of the relevant biological sex. For instance, a scheme promoting women in a male-dominated field may lawfully exclude trans women from eligibility.
• Single-Sex Services and Spaces: Service providers offering distinct services for men and women — including in contexts such as healthcare, accommodation, or criminal justice — must apply biological sex as the operative criterion.
• Associations and Occupational Roles: Single-sex associations and roles subject to genuine occupational requirements must also adhere to the biological definition of sex.

Crucially, the judgment does not erode the rights of transgender individuals. Those undergoing or having undergone gender reassignment remain fully protected under that distinct protected characteristic. The judgment’s effect is to delineate the structure of those protections more clearly — not to dilute them.

Conclusion

The Supreme Court’s decision provides critical clarity in a contested area of law. By confirming that “sex” under the Equality Act refers to biological sex, the Court has not altered the law but reaffirmed the statutory boundaries within which it must operate. The distinction between sex and gender reassignment — far from being merely semantic — is foundational to the internal logic of the Act and to the fair and consistent administration of rights across a range of legal contexts.

For practitioners, policymakers, and institutions tasked with interpreting and applying equality legislation, the judgment offers a definitive interpretive anchor. In a legal landscape governed as much by principle as by precision, such certainty is not merely welcome — it is indispensable.