I don't know Rishi Sunak, but "a man is a man and a woman is a woman" seems like a tautology to me, so how it's "'sickening’ and ‘ridiculous’" escapes me, except as making yet another statement into a "dog whistle".

Of course he probably doesn't mean it this way, but taking the performative definitions and removing sex from the definition, then there is no actual thing to reference other than back to the word. There's no definition available - it becomes a qualia as far as I can tell. Actually, in some ways less than that - it becomes a bit of a "no true scotsman" argument, or a "what is canon in franchise" sort of thing. Because the performance of a man or woman is basically whatever each individual person says it is. It can convey nothing that isn't a stereotype and is likely harmful.

Anyway, the terms become meaningless - and in general anything we cared about there was to me actually based in the sex, not the gender anyway.