For fear of merging several themes, I had reason to check the GG Equality policy. Surprise, surprise...no mention of sex as protected characteristic
www.girlguiding.org.uk/making-guiding-happen/policies/girlguiding-policies/equality-and-diversity-policy/
Presumably, they argue it is because of their policies re trans girls but even if you tolerate that (dodgy as s158 positive action and schedule 16 single characteristic association require the participants to share the same protected characteristic), there is nothing about, for example, sexual harassment (which does not depend on the sex of the perpetrator/victim).
It certainly was not written/checked by a discrimination lawyer