LONDON

In a landmark case, the UK Supreme Court ruled Wednesday that the definition of “woman” in the Equality Act is based on biological, not acquired sex.

“The definition of sex in the Equality Act 2010 makes clear that the concept of sex is binary, a person is either a woman or a man,” the judges said in an 88-page ruling.

While the court ruled unanimously that sex-based protections under the Equality Act do not apply to trans women, Judge Lord Hodge said the decision should not be seen as disadvantaging transgender people, who have protections under other laws.

The ruling stressed that interpreting sex as something that can be legally acquired would create “heterogeneous groupings” by cutting across definitions of man and woman in the Equality Act in an “incoherent” way.

Wednesday's decision follows a long-running legal battle between the Scottish government and the group For Women Scotland.

The Scottish government had argued that transgender people with a gender recognition certificate are entitled to sex-based protections, while the group maintained that those protections apply only to people born female.

“Sex is real and women can now feel safe that services and spaces designated for women are for women, and we are enormously grateful to the Supreme Court for this ruling,” For Women Scotland co-founder Susan Smith said outside the court, according to the BBC.

The BBC also reported that a UK government spokesperson said the ruling “brings clarity and confidence for women and service providers.”