EA2010 does not apply to WR1992 (Schedule 22).
WR1992 mandates provision for men and women (birth sex) separately.
WR1992 does not mandate policing of employees' toilet use.
Croft etc gave a discretion to employees to permit male employees to use female facilities in exceptional circumstances.
There is no need to consider medical treatments, birth certificates, GRCs etc because that would be unworkable.
T considered that complainant was not disadvantaged because there was a small number of women and transwomen, it was a secure, controlled environment, and there was plenty of unisex provision of good quality: the harassment claim thus failed. This was a fact finding so not appealable, but that does mean a claimant with different facts could have won.
There's a separate legal argument, that it's illogical not to interpret WR1992 on all fours with Schedule 3 EA2010 ie single-sex facilities at work must be single-sex to keep their status as exempt from liability under Schedule 22 EA2010. This removes employer discretion and obliges them to police toilet use. A closely related but not identical argument is that mixed-sex toilets disadvantage women more than men, leading to direct sex-discrimination which could similarly undermine Schedule 22 exemption from liability (on the basis that it goes against the spirit of WR1992 to do something which it was arguably designed to prevent). These arguments apply irrespective of the facts of a particular case.
The GLP JR application covers some of the same ground and is pending a decision.