As FarNorth pointed out, clothes have nothing to do with the sex of the wearer. Buying in to the idea that ‘woman in trousers and man in dress’ is radical suggests an adherence to gender norms. Yes, it’s unusual (well, the man in a dress bit is) but the act of wearing a dress doesn’t make Izzard a woman any more than wearing trousers makes women into men.
Izzard, in common with many transpeople, has had neither surgery nor hormones, so remains very firmly in the sex he was at birth (and that assumes that there is a possibility of changing sex using those methods). How, in that case has he ‘become a woman’ on the days he decides he is ‘girly’?
How do transwomen (I understand that Izzard does not claim this status for himself) ‘become women’? What does it mean to ‘be a woman’ if hormones, gametes, socialisation, dress (or heels) or biological makeup are deemed irrelevant, and if we are not to insist that both sexes stick to socially determined gender norms in order to hang on to their birth sex identification? I would really like an answer to this, as it is at the heart of so much of the conflict surrounding this issue.