Sport England's equality and diversity action plan leaves out sex as a protected characteristic.
https://www.sportengland.org/media/13465/diversity-6-2.pdf
Sport England's safeguarding guidance (delivered through the Child Protection in Sport Unit) also leaves it out (co written by the NSPCC who have also been reluctant to talk about trans issues):
https://thecpsu.org.uk/media/445554/webcpsustandards-final-2.pdff_
I've tweeted SE but not had a reply yet. You can find me on Twitter (same as my user name here) or contact them yourselves.
This is important because all sports bodies will look to SE for guidance. It's one of the foundations on which they will decide their own policies on women and girls in sport.
TIA 