How a battle over defining a woman ended up in the UK’s highest court

Judges will rule on whether trans women should be considered female under the 2010 Equality Act

The verdict decided by judges could have far-reaching ramifications on how single-sex spaces operate (Aaron Chown/PA) (PA Archive)

A lawyer fighting to establish what it means to be a woman has argued in the UK’s highest court that sex is an “immutable biological state”.

Aidan O’Neill KC, acting for campaigners in Scotland, made the arguments during the Supreme Court’s hearing of a legal challenge over the definition of what it means to be female.

The landmark case - which began on Tuesday - follows an ongoing debate between the Scottish government and campaigners.

The verdict will determine whether trans women should be considered female under the 2010 Equality Act as the case seeks to decide if sex amounts to the biological sex you are born with or your gender identity in the eyes of the law.

It could have far-reaching ramifications across the UK on how single-sex spaces operate and human rights campaigners have raised fears the case may impact trans women’s rights and their ability to challenge discrimination.

Mr O'Neill, representing For Women Scotland, said: “In the Equality Act, sex just means sex, as that word and the words woman and man are understood and used in ordinary, everyday language, used every day in everyday situations by ordinary people”.

He urged the court to take account of “the facts of biological reality rather than the fantasies of legal fiction” and to uphold the appeal.

He added: “Our position is your sex whether you are a man or a woman or a girl or a boy is determined from conception in utero, even before one's birth, by one's body.

“It is an expression of one's bodily reality. It is an immutable biological state.”

What is the case about?

This case ultimately centres on the question of whether women with gender recognition certificates which state that they are female should be entitled to protections established under the 2010 Equality Act.

The Scottish government has said anyone with a certificate stating they are female is a woman.

The Gender Recognition Act of 2004 states that getting a gender recognition certificate constitutes a change of sex “for all purposes”.

Meanwhile, the Equality Act of 2010 safeguards specific groups from being discriminated against at work and in society - with an individual’s sex and gender reassignment considered as protected characteristics. The legislation defines a woman as “a female of any age”.

How long has it been going on?

2018: Legislation entitled Gender Representation on Public Boards (Scotland) Act was passed in Scotland in an attempt to get more women on public sector boards. This law included females who were “living as a woman” and were wanting to or about to embark on changing their gender.

The campaign group For Women Scotland issued a challenge against the legislation in court.

2022: After several appeals, For Women Scotland won. The campaign group persuaded judges that the Scottish government's attempt to broaden the definition of women to include trans women infringed equality law.

Although the Scottish government was forced to change their legislation, they still released new statutory guidance alongside the bill saying they would see women as those with gender recognition certificates stating they are female. The guidance stated that under the 2018 Act the definition of a woman was the same as that set out in the Equality Act 2010.

For Women Scotland disputed their guidelines but lost.

December 2022: Judge Lady Haldane reached the verdict that the definition of sex was “not limited to biological or birth sex” and those who had a gender recognition certificate could be included. 

November 20024: For Women Scotland challenges this decision at the Supreme Court.

What could happen next?

Five judges - led by the court’s president Lord Reed - listen to the opposing arguments on Tuesday and Wednesday and then hand down a judgement at a later date.

The ruling could have a far-reaching impact on how trans women should be treated in the eyes of the law and whether trans women can claim they are being discriminated against under the Equality Act.

The landmark case could result in a range of places, including sports competitions, refuges for domestic abuse victims, sexual violence services, and hospital wards, being forced to change their policies towards trans women.

For Women Scotland do not see those with a gender recognition certificate stating they are female as women - they solely see sex in biological terms. Campaigners on this side of the debate argue single-sex spaces are under threat in the UK.

On the opposing side, human rights campaigners have raised fears trans rights will be eroded if For Women Scotland wins the case.

Amnesty International UK, a leading human rights charity who has intervened in the Supreme Court case, has argued gender recognition is a matter of human rights.

“Legal gender recognition as it works now is essential for trans people to enjoy the full spectrum of human rights each of us is entitled to, and live free from fear of discrimination,” a spokesperson said.

“Regardless of what we look like, where we come from or how we express our gender identities, human rights apply to everyone, and we all deserve to be treated with dignity and respect.”

Additional reporting by agencies