From a discrimination tribunal:
What does the law say about single sex toilets?
The EAT's decision in Miller has made it clear that tribunals will not accept that adequate toilet facilities are provided where someone may have to interact with someone of the opposite sex.
The Workplace (Health, Safety and Welfare) Regulations 1992 set out statutory obligations to provide separate male and female toilet facilities for employees. The regulations currently allow employers to install gender neutral facilities but only where they are in separate rooms that are lockable from the inside. That may change. In the summer 2023 the government launched a short technical consultation on changing the regulations to ensure that all new non-domestic public and private buildings will have to provide single sex toilets for women and men or a self-contained private toilet. The government hasn't yet published its response.
Full details of case here https://www.irwinmitchell.com/news-and-insights/expert-comment/post/102j048/failure-to-provide-a-toilet-for-the-exclusive-use-of-women-sex-discrimination