The Gender Recognition Act of 2004 specifically says that someone with a gender recognition certificate shall be considered in law to belong to their acquired sex. This is being reversed thanks to the UK’s Supreme Court ruling today that the legal definition of “woman” is based on biological sex.
Had the court allowed any trans people to give evidence or any doctors or scientists who work in the field of gender identity, they would have discovered two things. First, the purported “threat” to women’s rights posed by the existence of trans women does not exist. And second, the definition of “biological sex” is infinitely more complicated and harder to pin down than a simple matter of X or Y chromosomes.