
They say “hard cases make bad law“. What little case law there is about single sex spaces and transgender people’s access to them falls into that category.
Croft v Royal Mail was an employment case which considered the issue of toilets and changing rooms. It went to the Employment Appeal Tribunal and then to the Court of Appeal in 2003. The outcome is not popular with anyone, since it does not give a clear answer either way.
It says that
But it it also suggests that employers can not solve the issue by simply offering a unisex alternative. The Court of Appeal said that at some point a male person should be considered transitioned enough to gain access to women’s facilities, even if they had not ‘changed sex’, but it would not say what that point was.“acquiring the status of a transsexual does not carry with it the right to choose which toilets to use”
Lord Justice Pill, Court of Appeal

The case concerned a Royal Mail employee Nicolas Simpson, who later changed name to Nicki Simpson and then Sarah Croft while working as a van driver at the depot in Leicester.
Simpson, a father of three, and long-time cross dresser, had worked at the depot for 10 years before being diagnosed with gender dysphoria in 1997 and deciding to transition.
After a meeting with local managers in August 1998 when a ‘low key’ approach to transition was agreed, Simpson began to attend work “dressed as a woman” (as the tribunal describes it) and requested the use of the name Nicki. Management supported this by briefing colleagues about Simpson’s transition, and about their harassment policy. They offered Simpson use of the unisex disabled toilets “for the time being”. Regional management advised that Royal Mail were prepared to offer access to the female toilet facilities at an unspecified time in the future saying
“we have to consider two main issues, your own views and preferences, but also the views and preferences of our female employees”
Royal Mail
There is much more to read, please see link above.
