Britain's Supreme Court ruled Wednesday the legal definition of a "woman" is based on a person's sex at birth, a landmark decision with far-reaching implications for the bitter debate over trans rights.

In a win for Scottish gender-critical campaigners who brought the case to the UK's highest court, five London judges unanimously ruled "the terms 'woman' and 'sex' in the Equality Act 2010 refer to a biological woman, and biological sex".

However, the court underlined that the Equality Act also protected transgender people from discrimination.

The act "gives transgender people protection" through the protected characteristic of gender reassignment, but also protecting against discrimination in their acquired gender, Justice Patrick Hodge said handing down the verdict.