Is this HMP? “Mainstream” and “protection” are not terms I’ve ever known used.
The use of these terms suggests a different service, or private? Either way, most uk prisons don’t have the structure to be able to separate by offence. Of course, vulnerable prisoners will be sometimes kept on a VP unit or in segregation.
The poster was suggesting that they are automatically segregated by offence and that the offence itself is the indicator of their vulnerability. I don’t know what prison you used to work in but practically it’s not usually possible to keep them “strictly” separated.
And if that’s what PPs believe why are they all “give that man an OBE” and “let me thank and shake hands with that man” if it’s a given he’s also a sex offender? Bizarre.