when we are talking about sex segregated activities/places etc, the segregation is occurring on grounds of the protected characteristic of sex, and therefore using trans/gender reassignment/religion/age as an argument against sex segregated space is null and void, because none of those factored into the original reason for segregation?
This is the point that I continually scream from the rafters. If sex segregation is considered proportionate and legitimate, it is proportionate and legitimate for access to be determined by sex and for exemptions to be applied.
In terms of the GRC distinction, as a pp has stated, seeing as it is illegal to ask for a GRC, how on earth can appropriate access be monitored/checked upon.? Whilst I don't buy the argument that it is impossible to 'police' access (after all, people drive cars everyday without proving they have passed their test/have tax, insurance and an MOT) if people cannot be asked to prove their sex, any attempts to protect sex based rights are meaningless.