Why the definition of a woman has caused so much controversy
The term "woman" has been defined by the Supreme Court as only including biological women. But why did this debate head to the courts - and why has it been such a controversial subject?
Thursday 17 April 2025 14:00, UK
The Supreme Court has ruled on how a woman should be defined in UK law.
It's a case which stemmed from a legal dispute in Scotland - but the ruling on 16 April could have a profound effect on the rights of transgender women across Great Britain.
But why did this debate head to the courts, what exactly was the outcome and why has this been such a controversial subject?
What was the ruling for?
It was to settle a legal dispute between the Scottish government and the campaign group For Women Scotland (FWS) dating back to 2018, relating to the definition of a "woman".
Specifically, it related to two pieces of Westminster law: the 2004 Gender Recognition Act and the 2010 Equality Act.
The 2010 Equality Act is law which protects people from discrimination in the workplace and in wider society, and the 2004 Gender Recognition Act rules that those with a gender recognition certificate (GRC) have the legal right to live in their acquired gender.
Essentially, the Scottish government was claiming that under the Equality Act, the term "woman" included transgender women as well as biological women, and that they should have the same protections, because the 2004 Gender Recognition Act changes someone's sex "for all purposes".
FWS argued sex-based protections should only apply to people born female.
What was the outcome?
The Supreme Court ruled unanimously that the terms "woman" and "sex" refer to a biological woman and biological sex in the Equality Act 2010.
The ruling added that interpreting sex as "certificated sex" - through a GRC - would create "heterogenous groupings" by cutting across definitions of man and woman in the Equality Act in an "incoherent" way.
They said there would be an "odd inequality of status" between trans people who have a GRC and trans people who do not, with "no obvious means of distinguishing between the two groups".
Major development in an ongoing debate
Baroness Kishwer Falkner, chair of the UK's Equality and Human Rights Commission (EHRC), called the ruling "enormously consequential" - and there have already been calls to change policies, such as for the NHS to stop allowing transgender people on single-sex wards aligned with their gender identity.
The confusion and controversy over the definitions of sex and gender have been growing in recent years, not only in the UK but across the world.
Earlier this year, on his first day back in office, US President Donald Trump passed an executive order that called on the federal government to only recognise two genders - male and female.
Pro trans activists argue that if a biological male transitions, they should have the same rights as a biological female and be treated in the same way in law.
But female rights activists believe adopting this approach would endanger biological women and impede on their rights.
Scotland's push for trans rights - and the impact of JK Rowling
Scotland in particular has proved to be a microcosm of the kind of debates taking place across the globe, with the country's government pushing hard in favour of trans rights.
In 2022, Nicola Sturgeon's government passed a controversial gender recognition bill to make it easier for someone to legally change their gender, but it was ultimately blocked by Westminster.
Then in April last year, new hate crime laws were introduced in Scotland which make it illegal to "stir up hatred" in person or online over someone's transgender identity, sexual orientation or other personal characteristics.
Harry Potter author JK Rowling, who has lived in Scotland since 1993, has become one of the leading voices against the trans rights movement and the government.
She first entered the debate in 2019, when she supported a researcher who was sacked after tweeting that transgender people cannot change their biological sex.
The following year, she wrote an open letter about her reasons for speaking out, saying trans activism was impacting spaces such as women's prisons and rape and domestic abuse services. The author, who denies claims she is transphobic, said she wanted trans women to be safe, but not at the expense of cisgender women and girls.
She now predominantly posts to her 14 million followers on X about the issue, receiving a mix of heavy support and criticism.
After the Supreme Court ruling, she posted a photo of herself with a drink and a cigar, with the caption: "I love it when a plan comes together."
She has consistently clashed online with India Willoughby, Britain's first transgender newsreader and the first transgender co-host of an all-women talk show, ITV's Loose Women.
Willoughby accused Rowling of "grotesque transphobia" last year after the author referred to her as someone who was "cosplaying a misogynistic male fantasy of what a woman is".
After Willoughby expressed her "shock" at the Supreme Court ruling, Rowling twice called her a man.
The debate over trans rights has spanned all aspects of society, but has been particularly prominent in a few areas, including:
Prisons
Women's rights activists have argued trans women pose a danger in female prisons, while trans activists say trans women are at risk in male jails.
The issue has been particularly prevalent in Scotland, where a transgender woman convicted of raping two women while she identified as a man was briefly sent to an all-female prison, before safety concerns led to her being transferred to a male prison.
There has also been a high-profile employment tribunal centred around a female nurse who was suspended by NHS Fife after objecting to a transgender doctor using a female changing room.
Single-sex spaces
Spaces solely for women such as bathrooms, changing rooms and hospital wards have also been a contentious issue, with trans activists saying they should be allowed to use the spaces of the gender they identify as.
But the Supreme Court's ruling stated transgender women, even those with a GRC, can be excluded from single-sex spaces if "proportionate".
"If sex means biological sex, then provided it is proportionate, the female-only nature of the service...would permit the exclusion of all males including males living in the female gender regardless of GRC status," the five justices said in their report.
NHS officials have confirmed they will consider the ruling as they update guidance on same-sex hospital wards.
As it stands, NHS guidance states: "Trans people should be accommodated according to their presentation: the way they dress, and the name and pronouns they currently use."
In a statement after the ruling, a spokesperson for the UK government said: "We have always supported the protection of single-sex spaces based on biological sex.
"This ruling brings clarity and confidence, for women and service providers such as hospitals, refuges, and sports clubs.
"Single-sex spaces are protected in law and will always be protected by this government."
Women's sports
Trans women feel they should be allowed to compete in female sports and sporting categories, while others believe they have too many advantages from being a biological male.
There are different policies depending on the sporting event.
World Athletics, for example, excluded all trans women from female events in 2023, in a move the body's president Lord Coe said was to "protect the female category in our sport".
It came a year after the swimming world governing body FINA did the same.
During the Paris Olympics, the International Olympic Committee (IOC) repeatedly stated if your passport said you are a woman you can compete in women's sport - but left it to individual sports to decide on eligibility.
For context, transgender people can change their gender on their passport.
But there is new pressure on the IOC going into the 2028 Los Angeles Olympics after the US president signed an executive order banning trans women athletes from competing in female sports.
"In Los Angeles in 2028, my administration will not stand by and watch men beat and batter female athletes," he said.
The IOC has not said if it will abide by Mr Trump's order.
Football is still assessing what to do on gender policies, with a FIFA review ongoing for at least three years.
It is not an issue that has hit the top leagues yet, but the Football Association (FA) told Sky News that there are believed to be around 20 transgender women playing in women's amateur football in England this season.
There are concerns about trans women with physical advantages of having gone through male puberty injuring female opponents.