NancyDrawed's son: biologically a woman is an adult human female, but some people can be legally women without being biologically female.
That is true enough, but as ever the truth is not enough for the trans lobby. They want people to be women who are neither biologically female nor legally women. Most so-called transwomen are neither of these, after all, being men without a GRC.
This is why politicians do not want to say what this young man states so clearly; they do not wish to upset all those self-proclaimed transwomen who are neither biological nor legal women (many of whom, or their allies, fill posts within their organisations.)
Oh, and I would add to the '... some people can be legally women without being biologically female' something along the lines of '... just as some organisations can be legally persons without being biologically human -- like Asda, for instance.'
-- Just for clarification, and to get the emphasis right, you understand.