Supreme Court of the United Kingdom Rules That The Legal Definition of a Woman Is Based On Biological Sex

Joanna Blair • 20 April 2025

The Ruling

Wednesday 16th April 2025 marked a 'historic' day with the UK supreme court displaying common sense to the world and Great Britain. Five wise judges ruled unanimously and issued a definitive ruling for what a woman is with that 'the terms "woman" and "sex" in the Equality Act refer only to a biological woman and their biological sex' (2). Thus, the legal definition of a woman in the Equality Act 2010 does not include transgender women who hold gender recognition certificates (GRCs) or certificates to say they have changed gender (2).

The case was brought to the supreme court by the gender-critical campaign group For Women Scotland which is financially funded by the famous Harry Potter Book author, JK Rowling after two Scottish courts rejected its arguments that the Equality Act’s definition of a woman was limited to people born biologically as a female (2).

What Does This Mean For Trans Women?
This could lead to greater restrictions on the access for trans women to services and spaces reserved for women (2). The judgement means that it is lawful to exclude biological males from female only services such as medical services and single sex spaces including changing rooms and hostels (2).

With regard to sport, governing bodies are now compelled to reconsider their rules by banning transgender women from competing in women's categories (1). From now on, the Supreme Court Ruling will mean that the legal definition of a woman is likely to have implications for sport at all levels from the elite to the grassroots (1). According to Holt and Melley (2025), many businesses, sports clubs and other organisations highlight how it is too soon to know what the new ruling will mean in practice.

Despite the Supreme Court ruling, the General Medical Council (GMC)is pressing ahead with its new policy of making it voluntary for medics to record any data on their gender or sex (3). Thus, female patients will be unable to ensure whether they receive care from a doctor of the same sex, which is not a legal right but can be requested (3).

What Is a Biological Woman or Biological 'Sex'?

‘Sex’ can refer to (5):
1. A category (male or female).
2. A system (genes and hormones); with sex chromosomes XY for males and XX for females. Women primarily produce estrogen and progesterone and a small amount of testosterone. The two hormones luteinizing hormone (LH) and follicle-stimulating hormone (FSH) help regulate the menstrual cycle and ovulation in women. Men produce significantly higher levels of testosterone, with the testes being the primary site of testosterone production.
3. Phenotypic sex i.e. primary sex characteristics via external genitalia. Genital organs can be removed or modified via surgical and pharmacological interventions.

Supreme Court Ruling In Practice

Overall, the court ruling enables clarity, if a single-sex space, like a toilet or changing room is women-only, that means biological males who identify as women should not use it (4). It says instead that trans people should use their "powers of advocacy" to campaign for third spaces, such as unisex toilets (4).