Also worth noting that although the SC only ruled on the meaning of sex in the EA2010, it also said someone’s certificated sex doesn’t change for the purposes of other legislation if it would make that legislation incompatible or unworkable.
The Workplace Regs were put in place to implement an EU Directive about health and safety and deal with ‘propriety’. The Supreme Court recognised that females, as a biological sex class, have a health and safety interest in being separated from biological males and it’s difficult to see how interpreting sex in the Workplace Regs to include people with GRC’s would not render their purpose unworkable for the same reasons the Court identified in respect of single and separate sex spaces in the Equality Act. Plus, it would put the Workplace Regs at odds with the single and separate sex provisions in the Equality Act which would lead to absurd results – particularly if the same facilities are used by customers.
Good explainer here:
https://www.theretailbulletin.com/retail-solutions/legal-do-retailers-have-to-provide-single-sex-toilets-and-changing-rooms-for-their-customers-and-staff-19-05-2025/