It's two different topics with different backgrounds.
Women in prison in England/ Wales (UK but split as devolution etc) have been a topic for years and years. Feminists and other groups.
Around should so many be in prison. Things like. Nature of offences, backgrounds, acting for others, impact on families, all sorts of stuff.
There are various groups that have been raising it for years and it comes up every few years in media.
Separately
There is the concept of anti carceralism (is that a word?). It's made its way into more mainstream UK attention. Via things like, many trans orgs being anti carceral, the phrase anti carceral feminism etc.
This phrase and argument has been, like so many other concepts and arguments in the last few years. Picked up from USA where it makes way more sense. And just used here even though it's a totally different context.
The USA I'm sure we're all well aware has massive problems. Too many to list let alone go into but things like. That it's run as an industry. The output from the work done is a astonishingly large % of USA economic output. The racism, differentials in sentencing for similar crimes due to various factors about the person. The existence of eye wateringly long terms for relatively not huge crimes. The proportion of black men who will go to prison. The % of population in prison.
In short. Huge awful issues. That is what the anti carceral thing is/ was about.
Bandying it around often by those who just like sounding progressive/ edgy etc is devaluing it's meaning in USA. And makes no sense here.
So hth!