A prisoner died of burns injuries after accidentally setting himself on fire while smoking the so-called zombie drug Spice, a report has revealed.

The inmate at HMP Hewell, in Redditch, Worcestershire, "might have been saved" were it not for an "unacceptable" delay in responding to his cell bell.

Details of the death were revealed in the annual report of the Prisons and Probation Ombudsman.

A disciplinary investigation was subsequently opened.

Presenting her annual report, ombudsman Sue McAllister said psychoactive substances continued to be a "serious problem" in jails.

The report also found self-inflicted prison deaths in England and Wales have increased by 23% in a year.

The Hewell prisoner, who had been jailed for robbery, had a long history of drug misuse but had "failed to engage" with the support he had been offered, the report said.

In September 2018, the 31-year-old pressed his emergency cell bell and called for help but it was 16 minutes before an officer found him.

He was said to be conscious, but unable to comply with staff instructions, and had severe burns to most of his body.

The report found the prisoner "may not have reacted initially because he was under the influence" of the psychoactive substance.

He died two days later.

Ms McAllister said it was a "very tragic and very distressing" case that revolved around the delay in responding to the bell.

Disciplinary proceedings were started against a prison officer, who resigned. A hearing conducted in his absence concluded he would have been dismissed.

The report also found:

There were 91 self-inflicted deaths in England and Wales during 2018-19, up from 74 the previous year

The number of prison deaths increased by 6% to 334 in the financial year 2018-19

The number of deaths from natural causes dropped from 188 to 180 during the year

There were four homicides in prisons in England and Wales in 2018-19, down from seven the previous year

Image copyright Google Image caption The ombudsman will also investigate the death of a baby whose mother gave birth alone at HMP Bronzefield

The report also included details of a case in which a 75-year-old inmate at Channings Wood Prison, Devon, who could walk only with a stick, was handcuffed to two prison officers while he was taken to hospital in an ambulance.

The man, who was serving a sentence for sexual offences, had a pacemaker, high blood pressure, type 2 diabetes and had been diagnosed with a urinary infection.

The report said the man's risk to the public was assessed as high, "but... the risk assessment also noted that he could only move short distances, used a walking stick, needed help for all his care needs and had very poor vision".

Ms McAllister said it was one of "very many cases" in which elderly or unwell inmates were restrained, including some who were close to death.

She said such practices were "unacceptable" and "inhumane".

The ombudsman would be conducting an "overarching... extraordinary" independent investigation into the death of a baby whose mother gave birth alone, at Bronzefield Prison, Surrey, she added.

Prisons Minister Lucy Frazer said the government funding measures "to stop drugs which fuel violence and self-harm, improving support during the often difficult first few days in custody".

She also said almost 4,400 more staff had been recruited in the last three years".