Supreme Court confirms biological definition of sex under Equality Act 2010 – what this means for employers

Navigating a complex and sensitive area

Issues of sex, gender identity and trans rights can be highly emotive and often polarising, both within the workplace and in wider society. Employers are increasingly being asked to manage situations where legally protected characteristics, such as sex, gender reassignment and philosophical belief, may interact or come into conflict. Balancing the rights of trans employees, those who hold gender critical views, and the wider workforce is no easy task.

The Supreme Court’s ruling in the case of For Women Scotland v Scottish Ministers has prompted strong reactions in many quarters, but it also brings long-awaited legal clarity of the definition of 'sex' under the Equality Act. While the Court ruled that 'sex' means biological sex for the purposes of the Act, it was equally clear that trans people remain protected under the existing legal framework. The protected characteristic of gender reassignment offers robust legal safeguards against discrimination, harassment and victimisation, which are unaffected by the judgment. The judgment clarifies how the law distinguishes between sex and gender reassignment, but it does not diminish employers’ ongoing responsibility to ensure that their practices, policies and cultures are inclusive of trans people, in line with their obligations under the Equality Act.

How did this issue reach the Supreme Court?

In this case, the Supreme Court considered whether the term “woman” in the Equality Act 2010 includes a transgender woman who holds a Gender Recognition Certificate (GRC), or whether the Act uses 'sex' to refer only to biological sex.

The case arose from a challenge to the Gender Representation on Public Boards (Scotland) Act 2018 (2018 Act). The 2018 Act sets out measures to improve the representation of women on public sector boards and defines “woman” to include transgender women. For Women Scotland Ltd (FWS), a campaign group, argued that this definition went beyond the legislative powers of the Scottish Parliament, as it touched on the meaning of sex under the Equality Act 2010, which is a matter reserved to the UK Parliament.

The outcome

FWS initially lost its case in the Outer House of the Court of Session, but the Inner House upheld the challenge. In response, the Scottish Government revised its guidance to remove the broader definition and instead referred to the Equality Act 2010. However, the updated guidance also stated that someone with a GRC should be treated as having changed sex, based on a provision in the Gender Recognition Act 2004 (2004 Act), which says that a person with a GRC is to be treated as their acquired gender “for all purposes”.

FWS brought a further judicial review, arguing that transgender women with a GRC should not be included in the 2018 Act’s definition of “woman”, because the Equality Act should be interpreted as referring only to biological women.

This time, the Outer House rejected the claim, accepting that the 2004 Act provides a mechanism for changing a person’s legal sex, and that this should carry through to how sex is understood under the Equality Act. The Court found that the two Acts could work together without conflict.

However, the Supreme Court has now disagreed. It held that the provision in the 2004 Act which allows someone with a GRC to be treated as their acquired gender does not apply where this would make another piece of legislation unworkable or internally inconsistent. The Court found that this was the case for the Equality Act; in particular, the sections on pregnancy and maternity, sexual orientation, single-sex services, and other provisions that rely on a clear and consistent understanding of biological sex.

The Supreme Court therefore concluded that the terms 'woman', 'man' and 'sex' in the Equality Act 2010 refer to biological sex, not to an acquired gender, including where someone has a GRC or is in the process of obtaining one. Crucially, the Court emphasised that this interpretation does not affect the existing rights of transgender people under the Equality Act: they remain protected from discrimination under the characteristic of gender reassignment, and may also be protected through claims based on perception or association with their acquired gender.

What does this mean for employers?

The Supreme Court’s ruling clarifies that the protected characteristic of sex under the Equality Act refers to biological sex. This provides employers with greater legal certainty when applying sex-based rights and obligations. At the same time, the judgment brings into focus a number of areas that will now require careful consideration and sensitivity in practice. Many employees may be wondering how this affects their rights in the workplace. Employers will be cognisant of polarised views within their workforce on the Supreme Court judgment and therefore careful thought should be given to how employees are supported and what communications are made so that everyone’s rights are understood and protected. Employers should be prepared to offer reassurance and support, clearly communicating how the organisation continues to uphold inclusive values while applying the law consistently and respectfully.

In light of the judgment, employers may need to reflect on several key areas including:

• Access to single-sex spaces and roles, including toilets, changing rooms, sleeping accommodation and staff networks
• Policy and procedure updates, including equal opportunities, inclusion, and grievance or disciplinary processes
• Equality monitoring and reporting, including how biological sex and gender identity are recorded and communicated
• Managing professional relationships, particularly where staff hold different beliefs or experiences in relation to sex and gender identity
• Safeguarding organisational reputation, including ensuring public-facing policies and communications are lawful, clear and inclusive.

The ruling also intersects with the legal protection of philosophical beliefs, including those known as 'gender critical' beliefs. Employers must continue to balance freedom of belief with dignity and respect in the workplace, ensuring that any action taken is proportionate and based on conduct rather than belief alone. Equally, those expressing belief-based views must ensure that their behaviour remains respectful and does not amount to harassment or create a hostile environment for others.

The Equality and Human Rights Commission (EHRC) has issued a statement welcoming the Supreme Court’s judgment for the clarity it provides on the definition of 'sex' under the Equality Act. The EHRC noted that the ruling resolves legal and practical inconsistencies that had arisen from previous interpretations, particularly in relation to single-sex spaces and the rights of same-sex attracted individuals. The Commission has confirmed that it will update its Codes of Practice and relevant guidance, including on single-sex services, to reflect the implications of the judgment. In the meantime, it continues to emphasise the importance of protecting all characteristics under the Equality Act, including sex, gender reassignment and sexual orientation.

Learning points for employers

While the judgment clarifies that the term 'sex' in the Equality Act refers to biological sex, trans people continue to be protected under the protected characteristic of gender reassignment, including protections against discrimination, harassment and victimisation. The judgment also clarifies the legal definitions of 'woman' and 'man' for the purposes of the Equality Act and detailed analysis will be required to determine how this may alter the interpretation of rights dependent on such definitions such as in the context of equal pay and pregnancy/maternity rights.

At the same time, the ruling is a reminder of the need for thoughtful policy-making and respectful workplace cultures that support everyone. This is a complex and emotive area, and employers may benefit from seeking advice tailored to their specific context, particularly when balancing competing rights and navigating sensitive issues in the workplace.

For more information or advice, please contact Joanne Oliver in our Employment team on 07909 547 537, or complete the form below.