Mummy as far as I'm aware, the Equality Act means that someone with a GRC (very small number of people) which includes a diagnosis of gender dysphoria, would automatically be housed in the female estate. At the moment the way things legally stand, in cases of self ID there is freedom for case by case decisions, some of which have ended badly, see the newspaper reports of the TIM who was moved to a womens' prison following all due process and discussions following self ID and then had to be segregated for sexually harassing and assaulting women prisoners. Under current legislation the bottom line is also that exemptions can be made by legal sex (which includes people with GRCs) if the need is significant. IE we will not put this TIM with a massive record for rape and assault in a women's prison.
That's the current state of play.
The proposed change to law is that these exemptions would go. Anyone who self ids, no matter how casually, with or without the condition of gender dysphoria, would be the sex they say, and that would have to be respected in every single case, irrespective of the person's history or criminal behaviour. It simply would not be relevant. So yes, Ian Huntley would be one of the people benefitting.
Take alongside this the TRA lobby view that trans people cannot commit rape, due to the privilege/power imbalance: the worst a trans person can do is have non consensual sex with you; that trans people cannot be guilty of a crime (again the privilege power imbalance), that trans people with a history of sexual offending committed those crimes because of the emotional pressure of their being trans and they are therefore the victims, and putting them amongst other women will relieve their condition, and also the Action for Trans Health manifesto which demands the immediate pardon and release of all trans prisoners.
I wish I was making this stuff up.