Convicts serving indeterminate sentences for public protection (IPP) are turning to self- harm as they see no end to their detention, a new report has warned.
Figures show that for every 1,000 people serving an IPP there were 550 instances of self- harm - far higher than the rate for prisoners given fixed sentences, which is 324.
The controversial sentences were introduced in 2005 but scrapped seven years later by then justice secretary Ken Clarke who has described them as a "stain" on the justice system.
But more than 4,100 prisoners are still serving the "discredited sentences", which mean they can only be released once a parole board is convinced they are no longer a danger to the public.
The Prison Reform Trust charity, which carried out the research, said a lack of resources, parole board delays and poor management means prisoners are being left languishing in jail with no end in sight.
The charity said four out of five convicts given the sentence have served their minimum terms but are still stuck behind bars.
Peter Dawson, incoming director of the Prison Reform Trust, said: "This report shows the growing toll of despair the IPP sentence is having on prisoners and their families, years after its abolition. Urgent action is needed.
"The Government should convert these discredited sentences into an equivalent determinate sentence, with a clear release date, and provide full support to people returning to their communities.
"Only then will the damaging legacy of this unjust sentence finally be confined to the history books."