they can't use the gender neutral toilet because it will be too outing and it will breach their human rights
Addressed and dismissed in last week's judgment alongside the 'well she's taking her four year old son in there so .... random blokes can go in too!'
The judgment, as ProtectTheDolls has commented, has more or less brought the guidance in by the back door. And it's now going to be difficult for the employers if they don't say clearly to their staff, you are expected to use the space for your sex OR the mixed sex provision, and you may not under any circumstances use opposite sex single sex spaces. As confirmed is legal in that guidance Jolyon took to court to test.
Equally the judge addressed the issue of 'well what if we men just do it anyway' or 'it's all tooooo confusing' with a statement that reasonable people would get their heads around this and follow the rules.
It's going to need to be a condition of employment, with consequences for breaches. Men employees cannot harass women employees in a single sex space, or deny them a single sex space by walking into it and turning it mixed sex. Otherwise the employer may find the women employees taking them to court.