Use of toilets and changing facilities –staff who have declared their
trans status should be free to use the facilities appropriate to their self-
identified gender.
'should' is an important hedge. That 'should' does not give permission to use female only spaces because these are protected under EA10. They can access mixed sex toilets, and I think all schools ought to have at least one mixed sex toilet as a matter of course.
The guidance for what constitutes a mixed sex toilet is quite firm as described by the HSE. The TIMs, TIFs, NBs, and everyone else have always been free to use these ones.
(i think this may now be difficult to find but a couple years ago I probably downloaded it.).