in very exceptional circumstances
I take this to mean
- exclusion from places where women are vulnerable - undressing, sleeping etc
- exclusion from initiatives that are targetted at increasing participation of women in public life - in sport, in employment, in politics etc
- exclusion from services designed for and targetted at women
For instance, it would be wrong to exclude a trans identifying men from a lunch celebrating Women in Business. It would be right to exclude men who identify as women from being nominated for a Woman in Business award.
It would be wrong to exclude a boy who identifies as a girl from attending Harrow or Eton, or one of the other all-boy schools. It would be right to exclude them from an all-girls school.
It would be wrong to exclude a trans identifying man from a job in a nursing home. It would be right to exclude them from tasks dealing with the intimate care of frail, elderly women.