The meaning of “woman” and “female” in the Equality Act has become one of the most contested questions of recent years. Last week the supreme court settled it, in a landmark legal judgment that affirms the rights of women to the same level of legal protection afforded to other groups.

The Equality Act protects people against discrimination on the basis of nine protected characteristics, including their sex, race, sexual orientation and gender reassignment. The question at stake was whether “sex” means someone’s biological sex, or their “certificated sex”; in other words, should those who are male but who have a gender recognition certificate (GRC) be treated as a woman under equalities law?

The answer that the supreme court produced is no: because to do so would be to drive a coach and horses through Equality Act provisions aimed at protecting women, lesbians and gay men. The law is........

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