Thousands of trans rights protesters gathered in London’s Parliament Square on Saturday, days after the UK’s Supreme Court ruled that a woman is someone born biologically female, thereby excluding transgender women from the legal definition.

With unease growing over what the ruling means for the rights of transgender people, protestors came together for an “emergency demonstration”, with activists waving fags and holding banners with slogans such as “trans women are women” and “trans rights now”.

“It’s a terrifying time to have your rights taken away from you,” said 19-year-old transgender woman Sophie Gibbs. “I was disappointed to think that we could live in a society that seems so progressive now but is willing to make such a dangerous and harmful ruling.”

The UK’s Supreme Court ruled the terms “woman” and “sex” in the Equality Act 2010 “refer to a biological woman and biological sex” in a long-awaited judgement that was delivered on Wednesday. The ruling essentially means trans women who hold gender recognition certificates are not considered women in the eyes of the law.

The trans community are worried the landmark ruling could undermine their rights, and be a catalyst for further judgments that erode progress made in recent years.

The UK’s highest court has said transgender people remain protected from discrimination.

“It’s a Pandora’s box situation where I just think we allow certain things and then we essentially opened up the door to allow way more than we ever thought could be accepted or pushed through,” said Zuleha Oshodi, 29.

The head of the Equality and Human Rights Commission said the ruling will mean transgender women will be excluded from women’s toilets, hospital wards and sports teams.

Scotland’s First Minister John Swinney said Saturday that he “understands” the “hurt and anguish” trans people are feeling over the verdict, while accepting that the ruling must be followed.

In the latest census, some 116,000 people identified as trans in Great Britain. About 8,500 gender recognition certificates have been issued.

The Supreme Court ruling stemmed from a 2018 law passed by the Scottish Parliament that required at least 50% women on boards of Scottish public bodies. Transgender women with gender recognition certificates were to be included in meeting the quota.

The judgment was celebrated by groups including For Women Scotland, a gender-critical campaign group backed by JK Rowling, which says that women’s safety is threatened by allowing transgender women into single-sex spaces.