Just giving this one a bump.
And particularly this bit:
That felt quite decisive for me. It seems to demonstrate that the equality act defines sex as biological sex at least some of the time ... which would surely prevent the judges from concluding that Parliament intended to redefine it in terms of legal sex?
Presumably "some of the time" is enough for "all of the time" when it comes to the definition of a word. Its meaning must remain consistent once it has been agreed upon, otherwise the Act is unworkable at the most basic level. Therefore the intent is clear: sex means biological sex, not sex modified by a GRC.
In reality, it's likely that the TM in this weren't even considered when the law was made. However, good luck to anyone arguing that line of thinking - equally, the Scottish government sounded ridiculous when they tried to suggest its intention was to remove maternity rights from any pregnant TM. It's amazing really that a certificate doesn't change how biology works and that TM still can get pregnant. Who knew?