The aftermath of the Supreme Court’s ruling on the meaning of ‘sex’

In the landmark case FWS v Scottish Ministers [2025] UKSC 16, the UK Supreme Court (UKSC) centred on a pivotal question: how can the language used by parliament in the Equality Act 2010 (EA 2010), which protects both cisgender and transgender (trans) individuals from discrimination on the basis of ‘sex’, be interpreted in a way that is legally coherent, while remaining consistent with the Gender Recognition Act 2004 (GRA)? The GRA sets out the legal framework through which a trans person may ‘acquire’ a new legal gender or sex status ‘for all purposes’ (s.9(1)) (but subject to the provisions of other primary and secondary legislation (s.9(3)). This raises fundamental questions about how the two statutes interact in practice.

While the UKSC’s task was, at its core, a dry exercise in statutory interpretation (typically preserved for the most devoted legal nerds), the consequences of its decision have been anything but dull. It has further ignited fierce public debate, introduced areas of legal uncertainty that were once understood to be settled, and sparked widespread confusion beyond the courtroom. Significantly, it has caused widespread concern within the trans community, particularly among those who may not ‘pass’ as their acquired gender, about how they can navigate public life with dignity, without facing unlawful discrimination, including treatment that may now be erroneously perceived as justified in light of the decision and subsequent commentary.

Lawyers advising on the implications of this decision should resist any temptation to treat its application as straightforward. The EA 2010 is a complex and nuanced piece of legislation that has always required a careful balancing of rights, that balancing act continues to be central in its interpretation and application. The UKSC concluded that its interpretation “…would not have the effect of disadvantaging or removing important protection under the EA 2010 from trans people (whether with or without a [gender recognition certificate (GRC)]).” [248]

The decision 

The UKSC held that the EA 2010 is primary legislation to which the carve-out in s.9(3) applies and the EA 2010 therefore overrides s.9(1) of the GRA, which 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 the male gender, the person’s sex becomes that of a man and, if it is the female gender, the person’s sex becomes that of a woman).’

This means that under the EA 2010, a trans person’s ‘sex’ should not be understood to be their legally acquired gender (as acquired under the GRA), but rather their so-called ‘biological sex.’ The UKSC stated: “A person with a GRC in the female gender does not come within the definition of ‘woman’ for the purposes of sex discrimination in section 11 of the EA 2010.” [266] Therefore, under the EA 2010, a trans person, regardless of whether they hold a GRC, will be treated in law as the ‘sex’ assigned to them at birth, rather than the sex they have legally ‘acquired’ under the GRA. 

The rationale to the ruling

The judgment is 268 paragraphs, totalling 88 pages, as follows:

• Paragraphs [6 – 35] deal with the UKSC’s approach to statutory interpretation, together with the factual background (I won’t repeat the latter);
• Paragraphs [36 – 111] deal with the GRA’s history, interpretation and operation;
• Paragraphs [112-264] apply the UKSC’s interpretation of the EA 2010;
• A summary of the UKSC’s reasoning can be found at paragraph [265]; and
• Paragraphs [266 - 268] are concluding paragraphs. 

The UKSC placed considerable weight on the definitions set out in the Sex Discrimination Act 1975 (SDA), concluding that there was ‘no doubt’ parliament intended the terms ‘man’ and ‘woman’ in that Act to refer to ‘biological sex’ [51], [162]. It also held that this interpretation remained unchanged by the Sex Discrimination (Gender Reassignment) Regulations 1999. Going further, the UKSC found no indication that the EA 2010 altered the meaning of ‘man,’ ‘woman’ or 'sex' from that established in the SDA [162–164], affirming that these terms, in the UKSC’s view, continue to refer to ‘biological sex.’

In examining how the GRA operates within this context, the UKSC affirmed that s.9(1) of the GRA provides that trans individuals with a GRC are to be regarded as their ‘acquired’ gender, ie, the gender stated on their GRC, ‘for all purposes.’ However, s.9(3) allows this rule to be disapplied by provisions in the GRA itself, any other enactment or subordinate legislation [75]. Crucially, the UKSC held that s.9(3) of the GRA does not require legislation to explicitly disapply s.9(1); it is sufficient if applying s.9(1) would render a statute incoherent or unworkable. Since the EA 2010 does not expressly address the effect of s.9(1) of the GRA [158], the UKSC analysed the provisions in the EA 2010 relying on s.11 (which contains a definition of the protected characteristic of sex) to determine whether interpreting ‘sex’ as ‘biological’ (ie, sex assigned at birth) or ‘certified’ (ie, sex legally acquired under the GRA) would lead to incoherence or absurdity [159–161].

Applying this approach, the UKSC concluded that the relevant provisions of the EA 2010 are “unworkable” unless ‘man’ and ‘woman’ have a biological meaning. The UKSC repeatedly expressed concern that interpreting ‘sex’ in line with a trans person’s “certified gender” would effectively divide those with the protected characteristic of ‘gender reassignment’ into two sub-groups: those with a GRC and those without, thereby granting greater rights to those who hold a GRC. It also discussed the practical challenge this would create for duty bearers, who are generally not permitted to ask individuals whether they have a GRC due to it being a confidential document.

Taking all this together, these factors led the UKSC to conclude that a ‘certified sex’ approach would be unworkable in practice [198–203] when interpreting the meaning of ‘sex.’

A comment on the rationale

Although the judgment provides a detailed analysis of the approach to statutory interpretation and the history of relevant legislation, there are also some striking omissions. In particular, there is no human rights analysis, notwithstanding that the UKSC granted permission for Amnesty International UK to intervene specifically on these issues. 

Amnesty International UK’s intervention focused on: 

1. the human rights principles embedded in European Court of Human Rights (ECtHR) case law, such as Goodwin v UK (2002) 35 EHRR 18, which the GRA was designed to reflect, and which inform the scope of s.9 of the GRA;
2. European Union sex discrimination jurisprudence rejecting a purely biological definition of ‘sex,’ see Chief Constable of West Yorkshire v A (No 2) [2004] UKHL 21; and
3. the rights contained in the European Convention on Human Rights (ECHR) potentially engaged by the EA 2010’s ‘sex’ and ‘gender reassignment’ exceptions, particularly the exceptions contained in Schedule 3, paragraphs 26 to 28 EA 2010 (relating to separate and single sex services), and why, in their view, no incompatibility arises from the lower courts’ interpretation. 

The absence of any discussion of these issues in the UKSC’s judgment leaves significant unanswered questions about UK human rights law and the UK’s compliance with the ECHR.

The wider implications of the judgment 

Despite the UKSC repeating that its role was not to “adjudicate on the arguments in the public domain on the meaning of gender or sex, nor […] to define the meaning of the word ‘woman’ other than when it is used in the provisions of the EA 2010” [2], the judgment has sparked a flurry of public debate and has triggered swift and significant shifts in policy positions, demonstrating the powerful, political impact of the decision.

Perhaps one explanation for the significant far-reaching response to the UKSC’s decision is the Court’s extensive analysis across a wide range of EA 2010 provisions, including those relating to separate and single-sex services [211] - [221], communal accommodation [222] - [225], single-sex education [226] - [228], associations and charities [229] - [231], trans participation in sport [232] - [236], the public sector equality duty [237] - [244], and even the armed forces [245] - [246].

Much of the post-judgment discussion has focused on its implications for trans people’s access to ‘single-sex spaces.’ In assessing those implications, it is essential to remain within the legal framework of the EA 2010. I have been repeatedly asked, often with genuine anxiety, whether the judgment makes it a criminal offence for trans people to use single-sex spaces. Let me be clear: it does not. The UKSC’s decision did not criminalise such conduct. Claims under the EA 2010 are civil matters, heard in employment tribunals or civil courts. The EA 2010 does not create criminal offences, nor does it empower the state to prosecute individuals.

Crucially, the FWS judgment does not require a service provider to exclude trans people. There is a real risk that some providers may react hastily, misinterpreting the decision and undermining lawful access to services. As the UKSC made clear, trans people, regardless of whether they hold a GRC, remain protected under the EA 2010. Notwithstanding the judgment, the exclusion of a trans person will still need to be objectively justified as a proportionate means of achieving a legitimate aim should they challenge exclusion as being unlawful discrimination on the basis of ‘gender reassignment.’

The possible routes of challenge

This article won’t attempt to chart every legal challenge that may follow, but one thing is clear: this area of the law will continue to develop far into the future. 

One of the immediate challenges for service providers is the legal risk of discrimination claims whether they restrict access to biological women or adopt a trans-inclusive approach. For example:

1. A trans woman could bring a gender reassignment discrimination claim (and, where relevant, an Article 8/14 ECHR claim against public authorities) arguing she suffers a particular disadvantage when services are segregated by biological sex, especially if she is effectively excluded from accessing those services altogether or feels unable to safely access the service for ‘biological’ men. The service provider would need to justify this exclusion as proportionate and legitimate.
2. Conversely, if a provider introduces a trans-inclusive service, it is unlikely to qualify as a ‘single-sex’ service under Schedule 3 of the EA 2010. This opens the door to potential sex discrimination claims, for example, from a ‘biological’ man seeking access to a trans-inclusive women’s space. While Schedule 3 may not provide a defence, other provisions may be relevant to justify this approach as being lawful, such as Sections 23, 19(2)(d), and 158 of the EA 2010.

Put simply, there is no ‘risk-free’ option. In my view, the application of the ‘proportionality’ test in the EA 2010 is now set to become one of the central battlegrounds in litigation following this judgment. It is essential that service providers appreciate that the mere existence of Schedule 3, Paragraph 26 of the EA 2010 does not automatically justify the adoption of single-sex spaces or services. A decision to restrict access to services based on sex must be justified as being proportionate and these decisions must now be reconsidered in light of the UKSC’s interpretation of the definition of ‘sex’ under the EA 2010. 

Service providers must carefully balance the rights of all those who may need access to a given service. Any suggestion that this process has been made simpler following the UKSC’s decision is, frankly, detached from legal and practical reality. A nuanced and risk-based approach needs to be taken and advice should be sought where possible. 

This is what makes the Equality and Human Rights Commission’s (EHRC) recent stance so controversial. In the wake of its ‘interim update,’ the EHRC has been criticised for suggesting the FWS judgment provides a clear route to exclude trans people from spaces they were previously accessing. One would expect the UK’s national equality body to grasp the complexity of the EA 2010 more fully than most and to reflect that complexity in its guidance. Its current approach has raised serious concerns about how public bodies interpret and act upon judicial decisions, especially where the law is unsettled and politically charged, and whether this complies with their public law duties. Many observers have argued that the EHRC has moved prematurely to reflect the judgment in its guidance, and its response is now subject to possible legal challenge itself (see the Good Law Project pre-action letter dated 16 May 2025). 

A simple approach to remember among the noise

Amidst the political noise and legal debate, one thing remains clear: the EA 2010 is nuanced. Its application was never intended to be blunt or automatic, and this judgment changes neither that principle nor the need to tread carefully, especially as lawyers offering advice on the matter. 

Any attempt to impose an overly simplistic reading of the UKSC’s decision risks undermining the very balancing act at the heart of the EA 2010. In this evolving and deeply sensitive area of law, diligence must prevail. Context matters. Proportionality matters. And above all, rights must be weighed with care, not assumed away in the name of false clarity.