Back to Binary Basics

On April 16 2025, the Supreme Court of the United Kingdom (Supreme Court) delivered its decision on a fundamental question regarding the interpretation of the terms “sex” and “woman” under the Equality Act 2010 (EA) i.e., whether the EA includes trans women with a Gender Recognition Certificate (GRC) issued under the Gender Recognition Act 2004 (GRA). The Court unanimously held that, under the EA, the meaning of the word “woman” must be restricted to “biological” women, and does not include trans women, even those who have legally changed their gender under the GRA. The decision risks undermining the UK’s equality law framework and marks a troubling regression in gender rights.

Women’s rights v. transgender rights

For Women Scotland (FWS), an organisation purporting to act for women’s rights, initiated this case as their second judicial review, challenging statutory guidance issued under Section 7 of the Gender Representation on Public Boards (Scotland) Act 2018. The 2018 Act set a gender representation objective of 50% women in non-executive posts on Scottish public authority boards. Section 2 defines “woman” to include persons with the protected characteristic of gender reassignment who were “living as a woman” and undergoing transition processes. In their first judicial review, FWS successfully challenged this definition, with the Inner House ruling on February 18, 2022, that “transgender women” is not a protected characteristic under the EA and that the definition “impinges on the nature of protected characteristics, which is a reserved matter.” The Court declared the definition outside the Scottish Parliament’s legislative competence (paras. 15-18).

In response, the Scottish Ministers issued revised guidance on April 19, 2022, which operated on the premise that the Court had nullified the statutory definition of “woman”. The new guidance stated that under Sections 11 and 212(1) of the EA, and per Section 9(1) of the GRA, women with full GRC would count as women toward the Act’s 50% representation objective. The Scottish Government based this position on the notion that a trans woman with a full GRC has changed her sex in law from male to female (paras. 19-23). FWS then petitioned for judicial review in July 2022, arguing this revised guidance was unlawful and beyond devolved competence under Section 54 of the Scotland Act 1998 (paras. 21-22).

This raised the central legal question whether references to “sex”, “woman”, and “female” in the EA should be interpreted in light of Section 9 of the GRA 2004 to include women with a GRC. The case specifically addressed only the status of the small minority of trans individuals with full GRC(s) (approximately 8,464 people out of 96,000 trans people in England and Wales and 19,990 trans people in Scotland), whose sex remains in law their biological sex. In the later decision by the Outer House of the Court of Session, on December 13, 2022,  Lady Haldane had dismissed FWS’s petition, holding that Section 9 of the GRA 2004 could scarcely be clearer in changing a person’s sex for all purposes, and that the EA was “drafted in full awareness of the 2004 Act” (para. 27). The Second Division of the Inner House subsequently refused FWS’s appeal, confirming that a person with a GRC “acquires the opposite gender for all purposes” unless specific exceptions apply, and that persons with GRCs possess the protected characteristic of sex according to their GRC as well as gender reassignment (paras. 28-29).

Decoding the UK Supreme Court’s decision

The Supreme Court allowed the second judicial review and held that “sex” (and related terms) in the EA meant a binary idea of “biological sex”. The Court reiterated that under Section 9(1) of the GRA 2004, the acquired gender of a person with a GRC is recognised “for all purposes”, unless an exception under Section 9(3) applies. Section 9(3) provides that this rule does not apply where another enactment (like the EA) has made a specific “provision” that displaces this effect. The Court emphasised that such displacement does not need to be explicit or by necessary implication – contextual and purposive analysis may also suffice (para. 156).

The Court held that the terms “sex” and “woman” in the EA are to be interpreted as referring only to “biological” sex and “biological” women. To determine the intended meaning of “sex” and “woman” in the EA, the Court undertook a comprehensive analysis of its structure and purpose. It stressed the importance of predictability, clarity, and workability in equality law, which is grounded in group-based rights tied to shared experiences and biological realities (paras. 153-154, 171-172). The Court reasoned that many provisions in the EA 2010 – such as those dealing with pregnancy, maternity, breast-feeding, and health and safety exemptions – could only be coherently interpreted by reference to biological sex, since only biological women can become pregnant or give birth (paras. 177-188). It is crucial to note that the Court’s analysis was not confined to sections of the EA closely tied to reproduction, but explicitly recognised that single-sex spaces and women’s sports – such as toilets, changing rooms, hospital wards, and sports clubs – will function properly only if “sex” is interpreted as biological sex, with the judgment expected to have far-reaching consequences in these areas (para. 235).

The Court firmly rejected the Scottish Ministers’ argument for a context-dependent or variable definition of “woman” that could accommodate trans as well as cis women within some provisions of the EA (para. 190). It held that allowing different meanings of “woman” in different parts of the EA would violate the “principle of legal certainty” and undermine the statute’s consistency (paras. 191-192, 195). It also dismissed the claim that excluding trans women from the sex-based definition would deprive them of legal protection since trans people are already protected under the separate characteristic of gender reassignment in Section 7 of the EA (para. 198-201).

The Court also considered the practical and legal implications of accepting a certified sex definition. It pointed out that most individuals with the protected characteristic of gender reassignment do not have a GRC, and there is no outward means for duty-bearers (like employers or service providers) to know who does based on appearance. This would make the law extremely difficult to apply and could result in de facto self-identification, thereby undermining women-only spaces and protections (para. 203). For example, services like rape crisis centres, women’s shelters, or single-sex schools would no longer be able to operate meaningfully as women-only services if legal “sex” included trans women (paras. 211-218, 226-228).

Parliament said “all purposes”, Supreme Court said “well, actually…”

The Supreme Court’s decision marks a critical shift in the legal framework governing gender and sex-based rights in the UK. First, it challenges Parliament’s intention in the GRA by limiting the scope of legal recognition for transgender individuals with GRCs, contradicting the “for all purposes” provision and creating legal incoherence. Second, the ruling significantly diminishes the practical value of GRCs by establishing that they do not extend to the definition of “woman” or “man” under the EA, where “biological sex” is considered the statutory meaning, leading to a fragmented legal landscape and policy revisions by public bodies. Third, the Court’s narrow interpretation of “sex” as strictly biological fails to account for the complex lived realities of transgender people, ignoring both the social and physiological aspects of gender identity and creating a binary-centric framework that does not reflect real-world experiences.

The Great British Bake-Off of legal logic

One of the fundamental canons of statutory interpretation is to give effect to Parliament’s intention. The GRA was enacted as a direct response to the European Court of Human Rights’ (ECtHR) ruling in Goodwin v UK (2002), which found that the UK’s failure to recognise in law the acquired gender of “transsexual” people violated their rights under the European Convention on Human Rights. Parliament’s clear legislative intent was to enable trans people with a GRC to be legally recognised in their acquired gender “for all purposes”, thereby granting them access to the same rights and protections as cisgender individuals of that gender. A transgender person – including someone who has obtained a GRC – may retain biological and physical characteristics of what the Court seems to describe as “biological sex”. The true intention behind section 9(1) of the GRA 2004 was to provide legal recognition and an appropriate framework for such people for all purposes, without exception, unless expressly stated in the law. As the EA contains no express or necessarily implied exception to section 9(1), this should mean that the legal sex of a person with a GRC should be recognised as their acquired gender throughout the Act. However, the Supreme Court’s interpretation, in effect, reads the EA as cutting across the GRA in contexts concerning “sex” discrimination and “sex-related” services.

This judicial construction contradicts the clear legislative purpose of both Acts and undermines the comprehensive legal framework Parliament sought to establish to protect transgender individuals. By doing so, the Court creates legal incoherence where trans people are recognised in some legal contexts but starkly excluded in others. This approach is inconsistent with anti-discrimination protections, undermining the very purpose of the EA to ensure fairness and equality for all protected groups, and thus the principle of parliamentary sovereignty.

Too trans for some rights, not trans enough for others

In terms of gender recognition reform, the Court’s interpretation impacts the legal weight of GRC(s). While the GRC process remains in place – allowing individuals to change the “sex” on their birth certificate and be legally recognised in their acquired gender for many administrative and legal purposes – the Court has now drawn a clear boundary: This recognition does not extend to the definition of “woman” or “man” under the EA where “biological sex” is the statutory meaning. This shift has profound practical implications. Previously, obtaining a GRC was seen as the definitive legal step for trans people to be recognised in their acquired gender across all areas of life, including anti-discrimination law. Now, the Supreme Court’s decision means that, for the purposes of the EA, a trans woman with a GRC is not considered a “woman” in contexts where the EA’s sex-based provisions are triggered – such as access to women-only spaces, participation in women’s public boards, or eligibility for women’s quotas.

Moreover, the Supreme Court’s concern about practical implementation (see paras. 203, 211-18) that service providers cannot visually distinguish GRC holders creates a false dilemma that was previously addressed by the Scottish Court of Session, which recognised that many protected characteristics (including pregnancy, sexual orientation, and religion) are not visually apparent yet remain workable in practice. The Court’s rationale that recognising trans women’s legal sex would undermine women-only spaces relies on unsupported assumptions about safety risks rather than evidence. By prioritising hypothetical implementation concerns over Parliament’s clear intent in both the GRA and EA, the Court effectively creates a hierarchy of rights where practical convenience trumps the legal recognition explicitly granted by statute, an approach that fundamentally misunderstands how anti-discrimination frameworks routinely manage invisible protected characteristics through self-declaration.

The UK Court decision is likely to have a chilling effect. It has already prompted public bodies, such as the British Transport Police, to revise policies so that searches and other “sex-based” procedures are conducted according to the idea of “birth sex”. NHS officials and other service providers are also reviewing guidance on same-sex wards and facilities, with the expectation that trans women, even with a GRC, may be excluded from spaces now reserved for cis women. This creates a fragmented legal landscape where trans people are recognised in some contexts but excluded in others, diminishing the practical utility of the GRC.

Not beyond the binary

The Court’s interpretation of “sex” as strictly “biological”, excluding trans women – even those with GRC(s) – from the legal definition of “woman”, is narrow and binary-centric. This interpretation ignores the lived realities of transgender people, for whom gender “identity” is a deeply felt and integral part of their personhood, not merely a biological fact. It also seems to ignore the biological aspects for some people who are trans: hormonal and physiological changes, which are often visible. Instead, the Court’s reasoning prioritises an essentialist view of “sex” that fails to appreciate the bodily, social and legal complexities surrounding gender (see also Stein and Richardson).

As such, the Court fails to account for how transgender women may experience (intersectional) discrimination precisely because they are perceived as transgressing “sex” categories. The Supreme Court held that a transgender person who faces discrimination has multiple legal pathways for protection: They can claim discrimination based on the protected characteristic of gender reassignment if treated less favourably because they are trans, or they can claim direct sex discrimination if treated less favourably because they are perceived as being a woman (para. 253).

This approach, however, ignores the complex lived realities of transgender individuals whose experiences often involve both gender identity and sex-based discrimination simultaneously. The decision thereby entrenches exclusion and discrimination against trans people, rather than advancing equality in the way that the EA intended to do. Ultimately, the Court’s approach introduces profound ambiguities into equality law by suggesting that legal recognition of transgender people is conditional and partial. This threatens to legitimise discriminatory practices in healthcare, employment, and public services where transgender people already face substantial barriers. Extensive legislative intervention will be required to restore meaningful protections. More concerningly, the judgment may embolden efforts to restrict transgender rights further.