former police or prison officers, debtors, prisoners at risk of self harm and those who might be harmed by other prisoners. In some jurisdictions these prisoners are allowed to associate with each other, whilst in others they are held in regimes of strict solitary confinement, identical to those in punitive segregation, for the duration of their prison sentence. Prison management: managerial or administrative segregation is used as an internal tool for isolating prisoners variously defined as potentially dangerous, disruptive or otherwise posing a management problem, for example gang members. The rationale is that isolating such prisoners will reduce incidents of violence across the prison system and maintain prison order and discipline. This form of solitary confinement is usually imposed through an internal process governed by administrative rules. In some jurisdictions, prisoners are offered structured regimes starting with strict solitary confinement followed by gradually improved provisions and opportunities to engage with other prisoners, whilst in others, prisoners will be held in strict separation for the duration of their sentence. Where small group isolation is used, prisoners are held in single cells but allowed to associate with one to five other prisoners at designated times, usually during exercise periods. National security: protecting the public and/or national security is, and has historically been, used as a justification for placing those suspected or convicted of politically motivated crimes and of senior membership of major organised criminal gangs in solitary confinement. The rationale is to prevent the prisoner from contact with ‘terrorist’ or ‘subversive’ groups or organised crime gangs outside the prison, or to prevent the dissemination of State secrets. Convicted prisoners isolated on grounds of national security will typically spend their prison sentence in strict solitary confinement. Pre-charge and pre-trial investigation: suspects may be held in isolation without being charged whilst their interrogation is ongoing. In most jurisdictions such pre-charge detention is limited by law to a few hours or a few days, but some jurisdictions now have provisions for lengthier periods. In the UK, for example, terror suspects may be detained without any charge being brought against them for up to 28 days and, subject to a Bill introduced by the Government being enacted in its present form, this period may be extended to 42 days. Noting that the current provision of 28 days is already controversial, critics have called for this proposal to be scrapped. Pre-trial detainees, particularly those charged with crimes against the State, are also often isolated during the investigation or interrogation process. In some countries, most notably in Scandinavia, criminal suspects are also sometimes isolated pending investigation. The rationale in such cases is to prevent the detainee from compromising the investigation. In some cases detainees are isolated without access to legal counsel. This form of detention, called ‘incommunicado’, may be illegal under international law and is subject to special provisions33. Lack of other institutional solutions: prisoners are also sometimes held in solitary confinement because there are no appropriate alternatives available for housing them. For example, mentally ill prisoners may be isolated because there are no available secure hospital beds for them. These prisoners may not necessarily pose a danger to others or to themselves, but they are vulnerable to abuse and their behaviour may disturb or unsettle other prisoners and prison staff. Prisoners may also be segregated due to prison overcrowding whilst waiting for space to become available in a setting appropriate to their security classification. 26 Sourcebook on solitary confinement: The decision to place prisoners and detainees in solitary confinement