What is a woman? This has been one of the most vexed issues of recent years, one that has now been considered by the UK Supreme Court in a decision that made international headlines.
The case arose after the Scottish Parliament passed a 2018 law requiring some government boards to appoint “50% of non-executive members who are women”. Supporting government guidance declared that “woman” has the meaning given by the Equalities Act 2010 and that, by virtue of the Gender Recognition Act 2004, that meaning includes a biological male with “a full gender recognition certificate” which declares that their“acquired gender is female”.
The appellant, For Women Scotland, challenged this guidance.
The Supreme Court did not purport to define “woman” for all purposes, saying “It is not the role of the court to adjudicate on the arguments in the public domain on the meaning of gender or sex, nor is it to define the meaning of the word ‘woman’ other than when it is used in the provisions of the [Equalities Act].” Instead, it approached the case as an exercise in statutory interpretation, seeking to understand what Parliament meant when it passed that law.
The legislative history
The Court started by considering the Sex Discrimination Act 1975, the predecessor to the Equalities Act. There was “no doubt” that “woman” (and “man”) in the 1975 statute were defined by biology.
Almost 30 years later, the Gender Recognition Act was passed, allowing an adult to apply for a gender recognition certificate (GRC) if they could show that they had gender dysphoria, had “lived in the acquired gender” for two years or more, and planned to continue doing so “until death”. Where a GRC is issued, the Act provides that the recipient’s gender “becomes for all purposes the acquired gender”, and the Scottish government relied on this provision to argue that “sex” in the Equalities Act should be interpreted accordingly so that a person’s sex becomes their “acquired” or “certificated” sex.
However, that “all purposes” provision was expressly made subject to the terms of any other Act, meaning the Supreme Court had to conduct an in-depth review of the meaning of sex in the terms of the Equalities Act itself.
“Sex” in the Equalities Act
The Equalities Act forbids discrimination on the basis of named “protected characteristics,” which include sex, and gender reassignment. “Since sex as a protected characteristic is a ground for these legal rights,” said the Court, “it must be possible for sex to be interpreted in a way that is predictable, workable and capable of being consistently understood and applied in practice by [a] wide range of duty-bearers.”
At the outset, the Court considered that “sex”, “man”, and “woman” bore their “ordinary” meaning and were “plain and unambiguous”. Sex, defined in the Equalities Act by reference to being male or female, could only refer to “the biological characteristics that make an individual a man or a woman” because it is only biology that differentiates these two groups from one another. The Court also thought it significant that references to sex-based discrimination included discrimination on the basis of “breast-feeding”, “pregnancy, childbirth or maternity”—terms that could only refer to biological females and never to biological males “[s]ince as a matter of biology, only biological women can become pregnant”.
Further, said the Court, a “certificated sex” understanding would create “complex, heterogenous groups”—biological women plus biological males with a GRC (but not trans-identifying males without a GRC), on the one hand, and biological men plus biological females with a GRC (but not trans-identifying females without a GRC) on the other. This would undermine the logic of the Equalities Act, which is to protect features that characterise an entire group—in this case, “shared biology leading to shared disadvantage and discrimination”.
Other grounds of discrimination
The Court also thought that other protected characteristics in the Equalities Act shed light on the meaning of “sex”. One of those grounds, gender reassignment, was defined by reference to “changing physiological or other attributes of sex”. This could only be a reference to biological sex, said the Court.
Similarly, the protected characteristic of sexual orientation referred to orientation in relation to sex. The Court held,“[r]ead fairly, references to sex in this provision can only mean biological sex. People are not sexually oriented towards those in possession of a certificate.”
The need for practicality and coherence
Whether someone has a GRC is confidential, and others might not be able to tell from their appearance that their legal gender has been changed. The Court thought this was important because in practice, organisations might not be able to meaningfully distinguish between those who have a GRC and those who don’t, meaning “many organisations feel pressured into accepting de facto self-identification”. In other words, defining sex in terms of a certificate would make it impossible to draw meaningful sex-based distinctions where the law requires or permits this.
The Court considered a number of scenarios permitted by the Equalities Act, including provisions allowing for separate and single-sex services. If “sex” meant certificated sex, a club for lesbians would have to admit “trans women with a GRC (legal females who are biologically male and attracted to women).” Equally, that definition would mean a cervical cancer screening service could not be limited to biological women. The basic problem was that “it is likely to be difficult (if not impossible) to establish the conditions necessary for separate services for each sex when each group includes persons of both biological sexes.”
The Court also considered “women’s fair participation in sport”. The Equalities Act allows sports to be limited to one sex if they are “gender-affected”, meaning that average differences in “physical strength, stamina or physique” of one sex would disadvantage them if members of the other sex were also allowed to compete. Again, said the Court, this is “plainly predicated on biological sex and may be unworkable if a certificated sex interpretation is required”. Giving the example of boxing, it is “readily apparent (indeed, obvious)” that typical differences between men and women would disadvantage women.
Similarly, where the Equalities Act requires “positive action” to promote the interests of women, it would not make sense to treat this group as including biological men. That is because, said the Court, such a group “cuts across and fragments both biological sex and gender reassignment into heterogenous groups which may have little in common.” Here the Court gave perhaps its clearest statement on the importance of practicality and coherence:
the distinct discrimination and disadvantage faced by women as a group (or trans people) would simply not be capable of being addressed by [positive action measures] because the group being considered would not be a group that, because of the shared protected characteristic of sex, has experienced discrimination or disadvantage flowing from shared biology, societal norms or prejudice. Whereas the interests of biological women (or men) can be rationally considered and addressed, and likewise, the interests of trans people (who are vulnerable and often disadvantaged for different reasons), we do not understand how the interests of this heterogenous group can begin to be considered and addressed.
Protection for “trans people with or without a GRC”
Acknowledging that trans-identifying individuals are a “potentially vulnerable group” as well, the Court considered that defining sex as biological would not disadvantage this group or remove the protection of the Equalities Act.
First, they could still claim for direct discrimination. Someone is discriminated against if they are treated unfavourably because they are perceived to have a protected characteristic; they don’t need to actually possess that characteristic. Thus a “trans woman (a biological male with or without a GRC)” could claim sex discrimination if he was perceived as a woman and suffered discrimination as a result.
Second, UK law also allows someone to claim indirect discrimination “by association”; where a group defined by a protected characteristic is disadvantaged, someone who suffers the same disadvantage can claim discrimination “even if she does not share the characteristic in question”. Thus a man who identifies as a woman can claim indirect discrimination if he suffers the same disadvantage as women.
For these reasons, “a biological sex interpretation would not have the effect of disadvantaging or removing important protection under the [Equalities Act] from trans people”. To put it another way, “sex” did not need to be interpreted as “certificated sex” in order to protect members of this group.
The Court’s conclusion
Applying its reasoning to the Scottish government’s guidance, the Court said a certificated sex approach “changes the group to be represented.” Rather than promoting “representation on public boards of women (with their shared experience of disadvantage based on sex and overcoming such disadvantage)”, including “trans women with a GRC (in other words, biological men who are legally female)” would undermine the positive action measure.
“Sex” in the Equalities Act could only mean biological sex; defining it in terms of certificated sex would make the Act “incoherent and unworkable”.
The Scottish government’s guidance was therefore invalid.
Comment
The Court was careful to say that it was not defining the meaning of “woman” generally; rather, it was only defining the term for the purposes of the Equalities Act (and the guidance referencing that Act). Nevertheless, by clearly and unambiguously invoking biological realities and relating them to the law, the Court’s reasoning has wider implications.
The Court was obviously aware that the terms involved are highly contested and, in fact, that other apparently authoritative bodies had given them different meanings to the Court’s interpretation. The Court brought helpful clarity here, for example when it referred to various explanatory notes and guidance documents purporting to explain the meaning and effect of the Equalities Act and said:
Such aids can explain the meaning of a statutory provision which is open to doubt and can themselves alert the court to ambiguity in the provision, but they cannot displace the meanings conveyed by the clear and unambiguous words of a provision construed in the context of the statute as a whole.
When the Scottish government sought to rely on the explanatory notes to the Gender Recognition Act, the Court said:
this is a good illustration of why the use to which the courts should put explanatory notes is limited to the context of the legislation and the mischief to which its provisions are aimed.... There is nothing in the notes to suggest the department had undertaken the kind of detailed analysis ... that we have undertaken ....
Guidance issued by the Equality and Human Rights Commission was also invoked to support the argument that sex should have a certificated definition. The Court gave this short shrift, saying, “It is not for the EHRC to determine the meaning of sex in the [Equalities Act]. That is for the courts to do.”
This point is significant in New Zealand, where the Human Rights Commission treats discrimination against trans-identifying people as sex discrimination. An influential 2006 opinion from the then-Acting Solicitor General also concluded that sex discrimination in the Human Rights Act 1993 would be interpreted to include gender identity. But these are merely opinions about the law; per the Supreme Court, they are not the law itself.
That Court’s decision may influence the interpretation of our Human Rights Act, which defines sex to include “pregnancy and childbirth”—that is, in terms which relate inherently to biological women. At the same time, there is no explicit protection for “gender reassignment” or its equivalent, as there is in the Equalities Act, which may influence a local court to find that protection within the definition of “sex”.
Either way, the logic of this decision is highly relevant—not only to the courts, but to the Law Commission’s current review of the Human Rights Act and its coverage of trans-identifying people. The review report, and the Commission’s recommendations, are expected in the middle of this year.
For Women Scotland v The Scottish Ministers [2025]UKSC 16
