The UK Supreme Court has been told it would be capitulating to an “insidious and omnipresent” patriarchy if it allows gender recognition certificates to trump biological sex.

The long-running case about how “men” and “women” are defined in discrimination law is likely to have wide-ranging implications for single-sex spaces, including women’s refuges, prisons, changing rooms and hospitals.

For Women Scotland (FWS), argues that sex is a “biological fact”, which should trump recognition certificates that allow trans people to change their gender, as otherwise “nonsensical outcomes” arise.

Aidan O’Neill KC, representing FWS, urged the judges to “save the day for biological reality” rather than succumbing to “fantasies of legal fiction” that tilt rights against women and express a kind of patriarchy.

Referring to ‘menstruators’ instead of women, ‘birthing people’ instead of pregnant women and ‘bodyfeeding’ instead of breastfeeding were examples of that patriarchy, he said.

“Yet [trans woman] cannot menstruate, cannot get pregnant, cannot give birth, cannot breastfeed.”