A tiered system already exists  To some extent, prisoners will be categorized according to the offences they have committed. For example, those convicted of offences like armed robbery and many murders will start of at a higher level on the security system, which will mean restrictions in terms of activities, prison work and association with other prisoners.  A person convicted of a sex offence against children, or anything else particularly notorious, would be likely to be placed in some sort of protective custody. In the UK, this is done under Rule 45 of the Prison Rules [1] .  [1] England and Wales prison rules, available from  , rule 45