The UK Supreme Court has handed down a ruling that the legal definition of a woman is based on biology, not transgender ideology. This is undoubtedly a landmark ruling. While it does not overturn the legal protections that already exist for transgender people, it does clearly state that – for the purposes of the Equality Act – a person’s sex is binary and defined by biology. The decision has been hailed by those fighting to protect single-sex spaces and freedom of speech. But it is a blow to transgender campaigners.