This issue has become so emotive because people on both sides see it as a threat to their very identity.
The most recent census found there were 19,990 people in Scotland who were trans, or had a trans history – under 0.5% of the adult population.
The figure for England and Wales is also around 0.5% – 262,000 people told the last census that their gender identity and birth sex were different.
There is uncertainty around the true figures, with census returns thought to be overestimated – but what we know for sure is that 1,088 full gender recognition certificates were granted across the UK in 2023-24, up from 867 the previous year.
The figure has been rising since application costs were cut – and in the context of this case, it is people with full GRCs who are central.
Beyond this, equalities groups stress that there are a great many minority groups which are protected by the Equality Act, and see this case as potentially being the “thin end of the wedge” which could undermine their rights.
For trans people, they say it could erode the protections against discrimination they have under their reassigned gender.
If someone has a gender recognition certificate attesting that they are a woman, are they entitled to protection from sex discrimination under the Equality Act? Could they make an equal pay claim as a woman?
The UK’s first trans judge – who unsuccessfully applied to intervene, external in this case – is said to have pursued a pensions claim along those very lines against the Ministry of Justice.
Meanwhile women’s groups also say the ruling will have an impact on a large group – literally half of the population.
They say it could affect the running of single-sex services and spaces. Things like support groups for victims of sexual abuse can only legally justify excluding men due to the Equality Act’s protections.
Campaigners say everything from hospital wards to refuges and sports events might have to change policy or find themselves open to legal challenges based on the court’s ruling.
Lesbian groups – protected under “sexual orientation” in the 2010 Act – also say it could affect their ability to have exclusive clubs.