A UN torture expert has called on the UK government to urgently review all sentences imposed on prisoners held indefinitely under the “widely discredited” imprisonment for public protection (IPP) scheme.

Alice Jill Edwards, the special rapporteur on torture and other cruel, inhuman or degrading treatment or punishment, said the sentences, scrapped in 2012 but without retrospective effect, caused severe distress, depression and anxiety among both prisoners and their families.

On Wednesday describing the IPP scheme as “deeply flawed” and “regrettable”, Edwards said: “I’m particularly concerned about the higher rates of self-harm, suicidal ideation, suicide attempts and actual suicide among the IPP prisoner population. That in and of itself should really ring alarm bells and as to the damage that this is causing individuals. I do believe some of these sentences may have become – or are – inhuman and degrading.”

Her comments echo those of parliament’s justice select committee, which said last year that all IPP prisoners should be resentenced. This was rejected by the government.

Edwards said she had written to the government questioning “how the IPP sentencing system as it remains in its current guise is compatible with their human rights obligations, and, in particular the absolute prohibition on torture and other cruel, inhuman and degrading treatment or punishment”.

She said IPP prisoners are reportedly two and a half times more likely to self-harm than the general prison population, while government figures published in 2021 showed 65 IPP prisoners had killed themselves.

When released from jail, IPP prisoners can be sent back to detention at any time and often have been for relatively minor breaches of their licence. Whether they have to remain on indefinite licence is reviewed after 10 years out of jail although the government is considering whether that period should be halved.

More than half – 1,597 – of the remaining 2,909 IPP prisoners, as of 30 June, have been recalled to custody.

Edwards said that for years there had been insufficient and inappropriate resources to manage IPP prisoners effectively, with few having access to the rehabilitation programmes needed to demonstrate a reduction in their risk to the public.

“Without these safeguards, we are left with the mess that is the UK’s IPP system, where people are held without being able to prove that they deserve to be released,” she said. “It is therefore not surprising that many IPP prisoners are in a much worse mental state than at the time they were sentenced.”

She stressed that it was not acceptable for the UK government to cite resource shortages in an attempt to justify deviation from its human rights obligations.

A Ministry of Justice spokesperson said: “This government has already reduced the number of IPP prisoners by three-quarters since 2012 and is providing further support to help those still in custody progress towards release. We are carefully considering what additional measures might be put in place.”