The government are currently consulting on changes to the Gender Recognition Act to make getting a Gender Recognition Certificate a simple process of self-declaration. One of the areas this will have the most impact is prison placements.
Prison instructions for trans prisoners in the UK can be downloaded here - scroll down to '17/2016 The Care and Management of Transgender Offenders'.
The prison service go by legal sex, first and foremost. They're not allowed to ask to see a GRC but they can ask for a birth certificate (the sole remaining thing a GRC is good for). If a prisoner has a female birth cert (original or obtained via a GRC) they will be housed in the female estate unless they present an exceptional risk, in which case they may be moved to a men's prison, purely because this is where the facilities are. They will still be housed separately from men and will be accommodated in line with PSI for female prisoners. TW prisoners with a GRC are treated as female in all circumstances.
There is case law directly referenced in the prison rules linked above that says that even if a tw is in prison for attempted rape, if they have a grc and hence a bc that says 'female', they must be sent to a women's prison. The bar is very low as we have seen in various cases that have made mainstream media.
Only for trans prisoners without a GRC - i.e. those who are legally male - are decisions made on a case by case basis. And the Transgender Case Board are no fools, which is why all those self ID trans sex offenders are still treated as male prisoners in the male estate.
Changing the GRA to a self-ID process would allow all of them to be treated as female. The vast majority would have to be moved to the female estate, with only the few exceptionally dangerous ones remaining in the male estate, but housed there as female prisoners.
Frances Crook, executive director of the Howard League for Penal Reform, said:
‘some men with a history of extreme violence and sexual violence against women have found a new way of exercising aggression towards women. These men are not transitioning because they like women and want to be a woman, but in order to exert a new kind of control and dominance over women, a sort of infiltration.
You can participate in the GRA consultation here. It's open until 19 October so there's no rush, it's worth reading through the documents properly and researching anything you're not sure about.