The number of prisoners taking their own lives in segregated units is at its highest for nearly a decade, the Prisons and Probation Ombudsman has said.
Nigel Newcomen (pictured) said "segregation", in which an inmate is removed from association with other prisoners, should only be used in exceptional circumstances.
He expressed concern that several offenders identified as at risk of self-harm or suicide had been isolated in this way.
Mr Newcomen said: “Segregation is an extreme and isolating form of custody used for prisoners who have misbehaved or who cannot be kept safely in normal prison accommodation.
“It inherently reduces protective factors against suicide and self-harm, such as activity and interaction with others, and should only be used in exceptional circumstances for those known to be at risk of taking their own life.”
Charity the Howard League for Penal Reform has intervened in a “seminal” Supreme Court case brought by two segregated prisoners who claim their human rights were breached.
A judgement in this case is expected next month.
Frances Crook, the charity’s chief executive, said: “The Howard League is concerned by the informal use of solitary confinement, which is rife across the system and is a punishment particularly inflicted on children.
“We have succeeded in securing an investigation by Hounslow Local Safeguarding Children Board into the widespread use of solitary confinement of children in Feltham prison and hope that this will set a precedent to put a stop to the practice across all prisons holding children.”
A Prisons Service spokesman said: “Any death in custody is a tragedy and reducing the number of self-inflicted deaths in prison is a key priority.
"All deaths in custody are fully investigated by the independent Prisons and Probation Ombudsman and we have accepted the vast majority of their recommendations.
“Prisoners are segregated for their own safety and the safety of others and the use of segregation is carefully managed.”