Prior to 2015, the term natal female/male was widely used in academic publications and in information relating to trans issues (e.g. the Tavi's website). This was replaced by using 'cis' and trans and, wherever possible avoiding referring to sex. Where it was referred to, definitions weren't provided and it was paired with the word 'assigned' (or coercively assigned) - making the need for a clear definition more evident. The narrative at this time was always along the lines of, 'having consulted with the trans community/service users, these are the terms that they have asked us to use'.
Cass used the term 'sex registered at birth', I imagine this was an attempt at compromising as far as she felt appropriate. Not using 'natal sex' or 'assigned at birth' but something in between.
The ongoing battle seems to be between those seeking the terminology used to be clearly defined and as objective as possible and those seeking to create ambiguity on the grounds of reducing distress and/or making it easier to undermine sex as a category.
'Biological sex' is a relatively new entry. I want to know how it differs from 'natal sex', which worked well for a long time. If political parties and other institutions are returning to a definition of sex based on material reality, why was 'biological' needed? Why didn't we return to 'natal'.
We can speculate, but this needs answering. I have zero hope of getting a clear answer from Labour. I think the best way to address this is for the term 'natal sex' to be reclaimed and for GCs to use it consistently and not go along with the 'biological' term that seems to be the terminology politicians seem to have plumped for.
E.g. 'So, Kier, you are saying that natal females will be able to X and not face legal challenge' .
Whatever their game, if there is indeed a game, 2 can play it. We can just use the term natal whenever they use biological. We can check that they agree with our interpretation.