An elderly prisoner with dementia was kept handcuffed in hospital until shortly before his death.
The 77-year-old was attached to an officer via an "escort chain", which has a handcuff at each end, for two days while he was in hospital with pneumonia.
He began to have serious breathing difficulties, at which point one of the escorting officers called the prison and asked for a review of the need for restraints, a summary of the episode published by the Prisons and Probation Ombudsman said.
Referring to the prisoner as Mr D, it went on: "The prison made no immediate change. Minutes later Mr D became unresponsive and the officer removed the escort chain. He was pronounced dead shortly afterwards."
The inmate had suffered from diabetes, rheumatoid arthritis and poor vision when he first arrived in prison, before he developed heart disease and kidney disease. He suffered increasing memory loss, leading to a diagnosis of moderate dementia.
His mobility also deteriorated, meaning he needed crutches or a wheelchair and was only able to take a few steps "at best".
The episode was revealed as the ombudsman Nigel Newcomen published a bulletin on lessons that can be learned from investigations into deaths of prisoners with dementia.
Mr Newcomen said: "In my investigations, I have frequently been struck by how ill-prepared prisons were to deal with this new challenge, essentially because they were designed to meet the needs of younger people and not chronic age-related conditions."
Elderly and infirm prisoners often need to travel to and from hospital for appointments and treatment. When a prisoner leaves the prison, a risk assessment is conducted to decide whether the use of restraints is appropriate.
The report said: "Despite making numerous recommendations about restraints, and publishing a learning lessons bulletin on the topic, we continue to find too many cases where restraints have been used inappropriately on infirm and terminally ill prisoners, including those with dementia."
The number of prisoners aged over 60 is projected to increase from 4,100 in 2015 to 5,500 in 2020. Longer sentences and more late-in-life prosecutions for historic sex offences are seen as two of the main drivers for the shift.
Mr Newcomen added: "Things are beginning to move in the right direction in some prisons, with examples of good practice, but there is still a long way to go.
"The Prison Service badly needs a properly resourced national strategy for its rapidly growing population of older prisoners, to guide its staff in their management of age-related conditions such as dementia."
Peter Dawson, of the Prison Reform Trust, said: "Prisoners are entitled to the same care in prison as they would receive in the community. They should not be subject to inhumane or degrading treatment due to a lack of preparedness by the prison service."
A Ministry of Justice spokesman said: "We recognise the issue of dementia in our prison population and are committed to ensuring that older prisoners are treated fairly and that aspects of the regime are suitable, available and accessible.
"Decisions on restraining a prisoner are based on their risk to the public.
"This is subject to regular review, in particular in response to any change to the prisoner's health."
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