Following the decision of the Supreme Court in For Women Scotland the SLSA blog received immediate submissions discussing different aspects of the judgment. The post below is the first of these responses. Further responses will be posted in the following weeks. If you would like to submit a blog on this topic for consideration and inclusion in this series, please email blogeditors@slsa.ac.uk. All blogs will be submitted to our normal processes of editorial review. 

By Temitope Omotola Odusanya, PhD, Lecturer (Assistant Professor) in Law & LLM Law Programme Course Leader, Robert Gordon University.

1. Introduction

Achieving gender parity, traditionally understood as the equal ratio of women to men in public, corporate, and political institutions, has been a cornerstone of equality policy in the UK and beyond. However, competing interpretations of “gender” and “sex” have generated legal and political contention, particularly regarding the inclusion of transgender women in female-targeted initiatives. On 16 April 2025, the UK Supreme Court unanimously ruled that, by the Equality Act 2010, “woman” and “sex” must be understood as biological categories determined at birth, excluding transgender women from female quotas on public boards. This judgment not only clarifies existing legislation but also raises critical questions about the viability of parity measures in an era of expanding gender‑identity recognition.

2. Legal Background: The Gender Recognition Act 2004

Section 9 of the Gender Recognition Act 2004 provides that “where a full gender recognition certificate is issued to a person, the person’s gender becomes for all purposes the acquired gender (so that, if the acquired gender is … female, the person’s sex becomes that of a woman)”. In practice, this has meant that holders of full Gender Recognition Certificates (GRCs) are legally recognised as their acquired gender across most areas of law. However, the Equality Act 2010 does not expressly define “sex” or “woman,” leaving room for diverging statutory interpretations.

3. The Supreme Court’s Ruling: Case Background

The case For Women Scotland Ltd v The Scottish Ministers arose after the Scottish Parliament amended the Gender Representation on Public Boards (Scotland) Act 2018 to count transgender women with GRCs toward female quotas. The campaign group For Women Scotland challenged this inclusion as beyond the Scottish Parliament’s competence under the Scotland Act 1998.

3.1 Judgment

The Supreme Court held that the terms “sex” and “woman” in the Equality Act 2010 denote biological sex at birth, and that expanding these definitions to include transgender women would conflict with the Act’s plain language and statutory scheme. The Court emphasised that, although “biological” does not appear in the statutory text, the ordinary meaning of “sex” corresponds with unambiguous biological characteristics and introducing a separate gender‑identity criterion would render the law incoherent.

4. Implications for Gender‑Parity Initiatives

Public boards, corporations, and political parties aiming to meet female‑representation targets must now count only those individuals assigned female at birth. Transgender women holding GRCs will be excluded from these metrics, necessitating recalibration of diversity data and potential revision of self-reporting guidelines.

4.1 Legal Uniformity Across the UK

By anchoring the definitions of “sex” and “woman” in biological terms, the ruling centralises authority over sex‑based protections, limiting devolved administrations from broadening these concepts in their legislation.

4.2 Impact on Transgender Rights

Although transgender individuals retain protection under the Equality Act’s separate “gender reassignment” characteristic, excluding transgender women from sex‑based quotas may fuel debates about the coherence of sex versus gender‑identity protections. Critics warn of potential exclusion from single‑sex spaces and the chilling effect on transgender participation in public life.

4.3 Immediate Real‑World Consequences

The Supreme Court’s decision has “immediate real‑world consequences,” clarifying who may access single‑sex spaces, such as restrooms, sports clubs, hospital wards, and prisons, by excluding GRC‑holders from the legal definition of “women”. While judges stressed that the ruling was “not a victory for either side,” trans leaders decried it as “an attack” that “calls into question their very identity”. While one campaigner expressed deep disappointment at the outcome, describing themselves as “gutted,” the ruling has been widely welcomed by others for its clarity. Supporters commend it for reinforcing the legal basis for single sex spaces and for restoring confidence in the consistency of equality protections.

5. Broader Context: Global Trends Toward Binary Definitions of Sex

The UK ruling is part of a broader international movement reinforcing binary legal definitions of sex. On 20 January 2025, U.S. President Donald Trump issued an executive order declaring that the federal government recognises only two sexes: male and female, as “not changeable,” rescinding several Biden-era LGBTQ+ directives. Similar restrictive measures have emerged in countries such as Hungary, reflecting a global resurgence of biological‑sex absolutism.

6. Discussion

The Supreme Court’s decision highlights a fundamental tension between biological‑sex protections, historically designed to safeguard women’s rights and privacy, and emerging frameworks of gender‑identity inclusion. While advocates for women’s rights welcome the clarity this judgment provides, transgender rights groups decry its exclusionary consequences. Future legislative efforts might seek to reconcile these competing values, perhaps by codifying distinct categories for sex‑based and gender‑identity protections or by developing inclusive quota systems that explicitly address non‑binary and transgender representation.

7. Conclusion

The UK Supreme Court’s affirmation of a biological‑sex definition of “woman” represents an epochal shift in equality law. It compels institutions to revise gender‑parity strategies and prompts urgent reflection on how best to harmonise sex‑based and gender‑identity rights. As global governments explore similar binary definitions, the challenge will be to ensure that the pursuit of parity does not inadvertently marginalise those it aims to include.