Legal Definition of ‘Sex’ in Equality Act Clarified in Recent Supreme Court Ruling

On 16 April 2025, the UK Supreme Court handed down a landmark ruling in the case of For Women Scotland v The Scottish Ministers [2025] UKSC 16.  The Scottish government defended its statutory guidance concerning the legal definition of sex under the Equality Act 2010, asserting that transgender individuals with a gender recognition certificate (GRC) should be counted as women under gender representation targets.

Ultimately, the Scottish government were unsuccessful, with the Court ruling that sex under the Equality Act applies to biological sex. This judgment carries significant legal and practical implications, and with it being such a divisive topic, opinions are split. While some praise the ruling for clarifying biological women’s rights, others fear it may undermine protections for transgender individuals.

Below, we examine the history surrounding this long-standing issue and comments from the Supreme Court. We then discuss reactions to the ruling, including those from the Equality and Human Rights Commission (EHRC).

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The Legal Dispute in For Women Scotland v The Scottish Ministers

Leading up to the Supreme Court ruling in For Women Scotland v The Scottish Ministers, there was a lengthy battle concerning the legal definition of sex. Issues arose after the development of the Gender Representation on Public Boards (Scotland) Act 2018, which aimed to improve female representation on public sector boards in Scotland.

While the aims of the legislation may have appeared straightforward, the inclusion of transgender women made the reality more complex. The Act stated that transgender women with a GRC would count as “women” to meet the 50% gender representation target. For Women Scotland contested this approach, arguing that the Scottish government had incorrectly interpreted the legal definition of “women”.

Consequently, central to the dispute was the legal question of whether the definition of “woman” in the 2018 Act conflicted with the Equality Act.

As the dispute rolled on, it made its way through various levels of the Scottish courts. In an initial separate claim, the Outer House upheld the Scottish government’s approach, but this was reversed by the Inner House.

After subsequent revisions to the guidance —that were still allowing individuals with a GRC to be treated as women— both the Outer and Inner Houses sided with the Scottish government in the current case. Running out of options, For Women Scotland appealed to the UK Supreme Court, which unanimously allowed the appeal, declaring the revised guidance unlawful.

What is the Legal Definition of Sex in the UK?

At the heart of the Supreme Court ruling was a question that has provoked widespread legal and societal debate: What is the legal definition of sex in the UK? In its unanimous judgment, the Court held that the terms “sex,” “man,” and “woman” as used in the Equality Act refer to biological sex, rather than acquired or certified sex.

It paid particular attention to the Gender Recognition Act 2004, which allows individuals to be treated as their acquired gender. While the Court recognised this right, it established that it didn’t override the Equality Act’s definition. If it did, the Court stated legal incoherence or inconsistency would arise.

How the Ruling Affects Key Protections Under the Equality Act

Specifically, the Court examined several Equality Act provisions, which required a clear and consistent definition of sex. Examples included matters relating to pregnancy and maternity, same-sex attraction, and single-sex services. It concluded that interpreting sex to include individuals with a GRC would render these provisions “unworkable” or contradictory.

For example:

  • Pregnancy and maternity protections apply to individuals who can and do become pregnant. Scientifically speaking, only biological women have the ability to do so. With this in mind, only biological women can, therefore, be afforded such protections.
  • Same-sex sexual orientation protections apply to individuals attracted to others of the same biological sex. So, a lesbian is a biological woman attracted to another biological woman. As such, expanding the definition of a “woman” could undermine the very concept of same-sex attraction.
  • Single-sex services apply where it’s necessary to provide spaces exclusive to one biological sex for reasons of privacy, dignity, or safety. These services are designed to meet the specific needs of individuals as defined by the sex they were assigned at birth. Consequently, allowing individuals born male to access female-only services could render the legal exceptions meaningless and compromise the purpose they were intended to serve.

In summary, the Supreme Court affirmed that the legal definition of sex under the Equality Act is biological. Whether or not an individual is in possession of a GRC is irrelevant. However, the Court was quick to emphasise that its ruling didn’t interfere with the legal protections transgender individuals currently enjoy. The protected characteristic of gender reassignment remains intact, with transgender individuals being protected from all forms of discrimination.

Reactions After the Legal Definition of Sex is Clarified

Outside the Supreme Court and following the ruling, the co-founder of For Women Scotland, Susan Smith, spoke to the media. She said, “Today the judges have said what we always believed to be the case, that women are protected by their biological sex.” She added, “Sex is real and women can now feel safe that services and spaces designated for women are for women, and we are enormously grateful to the Supreme Court for this ruling.”

The EHRC also released a statement, welcoming the judgment. It stated how the decision brought clarity to how “sex” applies under the Equality Act, resolving ambiguities affecting women’s rights.

However, while some praised the Court’s decision, others took a different view. Scottish Green MSP Maggie Chapman, a well-known advocate for transgender rights, stated, “This is deeply concerning…It could remove important protections and will leave many trans people and their loved ones deeply anxious and worried about how their lives will be affected and about what will come next.”

What Does the Supreme Court Ruling Mean Going Forward?

With the judgment passed, employers must act to ensure their policies and procedures remain lawful. Sex-based rights, including single-sex spaces and inclusion policies, must be applied with biological sex as the reference point. Be that as it may, other protected characteristics, such as gender reassignment, mustn’t be forgotten, with employers obligated to take reasonable steps to protect such individuals from unfavourable treatment.

While the case has left opinions divided, one thing is for certain: employers must tread carefully when handling protected characteristics. This is especially the case when such characteristics intersect, as was the case here with sex-based rights and trans inclusion. Should employers fail in their obligations and leave staff open to unfavourable treatment, claims could arise.

If you have any questions about your employment rights or the legal definition of sex, please reach out. It could be that your rights have been breached, or you have concerns that they will. Whatever the case, Redmans Solicitors are employment law specialists, and following a brief consultation, we can provide expert advice.

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