Lawyer here.
It is a long established legal principle that when drafting legislation, any words which are used in a sense other than their usual, bog standard, everyday sense need to be defined.
As I said in my previous post, the Gender Recognition Act uses the words "male" and "female" to refer to "genders" but fails to define "male", "female" or "gender". This would ordinarily be considered negligent drafting, but in this case I believe it was deliberate, given that the effect of the Gender Recognition Act is to allow an individual to be legally recognised as the opposite sex.
Why this conflation of sex and gender? And why the refusal to define gender?
The answer is actually quite simple. Gender isn't real. Sex is the only thing that actually exists. A piece of legislation allowing an individual to change their legal gender but not their legal sex would have no impact, because there are no situations where gender is a relevant or useful way of classifying people and so legal gender is not a concept that needs to exist in law.
Gender is based in stereotypes, which is why nobody can define it. If you try to define a woman other than by reference to biological sex, you are left with two things. Feelings, and fashion choices. So your indefinable, unprovable, subjectively experienced feelings, which are unique to the individual and therefore cannot ne used to divide the entirety of humanity into two groups. And high heels, lipstick and push up bras. Obviously the legislators who drafted the Gender Recognition Act could not define the "female gender" as "having womanly feelings and wearing a bra", because that would have made it clear how ridiculous the whole thing was. So they chose not to define their terms and hoped nobody would notice.
Then six years later the Equality Act came along, with its protected characteristics. Sex and gender reassignment were listed separately, and the section on sex even allowed for some circumstances where it would be legal and proportionate to exclude a trans person from spaces for the opposite sex (i.e. the sex with which they believe they identify) even if they had a gender recognition certificate and were therefore legally the opposite sex. So it is clear that the Equality Act did intend to differentiate between someone whose biological sex is female (who benefits from the protected characteristic of "sex") and someone whose biological sex is male but whose legal sex is female (who benefits from the protected characteristic of "gender reassignment").
Unfortunately the wording was not clear enough to prevent Lady Haldane from finding, recently, that the protected characteristic of sex includes legal sex, which is why urgent clarification is now needed so that biological women can have their protected category again, as was always the intention.
And this whole debacle shows, for me, firstly why allowing people to change their legal sex is a bad idea regardless of what the international human rights community believes, and secondly, why we need to resist this assault on language. Because the trans "rights" lobby have proven time and time again that if you give an inch, they will take a mile. Give them "woman", they will change the definition of "female" too. Give them "gender", they will change the definition of "sex" next.