It survives under the Gender Recognition Act 2004.
"Where a full gender recognition certificate is issued to a person, the person’s gender becomes for all purposes the acquired gender (so that, if the acquired gender is the male gender, the person’s sex becomes that of a man and, if it is the female gender, the person’s sex becomes that of a woman)."
https://www.legislation.gov.uk/ukpga/2004/7/section/9
It is only for purposes of the Equality Act 2010 that TWANW, because the word "woman" in the EA means "biological woman". So TWAW except when it comes to single sex spaces or sex discrimination. I think.