A Guardian investigation has revealed prisoners who are seriously and terminally ill are routinely chained in hospitals despite posing no security threat.

A prisoner who was clinically brain dead remained in handcuffs in an ambulance taking him to another hospital. Another severely disabled prisoner was also chained. Glenda Jackson, his MP, said the practice was "disgusting and horrific."

According to the prison service, inmates who require treatment at outside hospitals are risk assessed before decisions are made as to whether to restrain them or not. But a Guardian investigation shows the use of restraints to be the starting point for prisoners taken to hospital, irrespective of their medical condition.

Examples discovered include a prisoner, Michael Tyrrell, 65, dying from cancer and too weak to move; 22-year-old Kyal Gaffney, diagnosed with leukaemia, who had suffered a brain haemorrhage; and Daniel Roque Hall, 30, suffering Friedreich's ataxia, a wasting disease that has left him barely able to use his arms or legs. All three were chained in hospital and guarded by three prison officers each.

Tyrrell, who was nearing the end of a 29-year sentence for drug offences and regarded as a model prisoner, was taken to hospital from Frankland prison, near Durham earlier this year. His daughter Maria said she and her sisters were horrified to see their father in chains when they visited him in hospital. She said the idea of her father running away was absurd. "He couldn't even prop himself up in that hospital bed. I was pulling him up so he could breathe." The restraints were only removed hours before Tyrrell died.

Gaffney, died in prison in November 2011, three weeks after being convicted of careless driving under the influence. He had been taken from Hewell prison, Worcestershire after suffering a brain haemorrhage, following a diagnosis of leukaemia. Though unconscious, he remained handcuffed to a prison officer until doctors ordered a CT scan shortly before he died. At one stage, doctors considered transferring him to another hospital, but the three prison officers present argued they should go in the ambulance with him. Gaffney's sister, Justine told the guards: "He's in a coma and you still think you need to stop him escaping?" In the end, medical staff agreed to travel with just one nurse and two guards, but by then it was too late.

In August last year, Daniel Roque Hall was rushed from Wormwood Scrubs prison, London to University College Hospital and placed in intensive care. He was serving three years for drug smuggling. Roque Hall, who used a wheelchair, was also guarded by three officers around the clock. He lost two stone in seven weeks, suffered dramatic muscle deterioration and was diagnosed with thyrotoxicosis. In February this year, he was released by the court of appeal after his lawyers argued Wormwood Scrubs could not meet his complex medical needs.

Glenda Jackson, Roque Hall's MP, said it was "absurd that people who could never present a risk to anybody, such as my constituent who is severely disabled, is chained in hospital. I find the whole practice disgusting and horrific."

The prisons and probation ombudsman Nigel Newcomen told the Guardian the issue of inappropriate use of restraints on elderly, infirm and dying prisoners needs to be addressed. "While the prison service's first duty is to protect the public, too often, the balance between humanity and security is not achieved." he said.

Deborah Coles, co-director of Inquest, said the chaining of seriously and terminally ill prisoners is "a shocking abuse of power". Lord Ramsbotham, a former chief inspector of prisons, compared the practices exposed by the Guardian to the chaining of pregnant women prisoners in maternity wards – a practice that was stopped in the mid 1990s. "The previous director general of the prison service used to preach what he called the 'decency agenda'. Clearly, there are some prison managers who do not understand what either word means," he said

A spokeswoman for the prison service said public protection is top priority and prison governors have a duty to mitigate the potential risk to the public, medical staff and other hospital users. "All prisoners are risk assessed before being escorted to hospital to ensure security measures are proportionate and that they are treated with dignity and respect," she said.