A DANGEROUS prisoner took a fellow inmate hostage and threatened to kill him after being denied painkillers for his bad back.

Convicted armed robber Jay Williams told guards at Pentonville Prison he would “slice open” his cell mate’s throat unless he got the medication he wanted.

He also held a mock trial for his terrified hostage, interrogating him and saying: “I will be the judge and jury on this one.”

The siege only came to an end after riot police stormed his cell.

Williams was serving an indefinite sentence for public protection at the time, which he was handed in 2010 after a string of knifepoint shop raids.

The 38-year-old, previously of Military Road, Colchester, had been moved to Pentonville from HMP The Mount, in Hertfordshire, after taking part in a rooftop protest.

Details of his case emerged as judges at the Court of Appeal, in London, reduced his jail term for the hostage incident from eight to seven-and-a-half years.

The court heard Williams, a violent criminal with previous convictions for witness intimidation, robbery and making threats to kill, was suffering from chronic back pain at the time of the offences in March 2015.

After attending a medical appointment, he said: “Have I got to take a hostage to get what I want?” and made threats to “break limbs” in order to get the medication he wanted.

Prison officers managed to calm him down and returned him to his cell, but within an hour he had barricaded the door of his cell by overturning the bunk beds inside.

He also covered the window so officers couldn’t see what was happening inside and said he wanted to see the governor and get his medication.

His cell mate, an Albanian in his 20s who was on remand accused of rape, was in the cell with him and Williams threatened to harm him if his demands were not met.

He then told officers: “As soon as the door opens, I will slice his throat open and cut him open.

“I have nothing to lose and I can handle the 20 year tariff.”

Turning his attention to his cell mate, Williams started complaining about having to share with an alleged sex offender and conducted a mock trial.

The incident lasted for more than three hours, before six police officers raided the cell.

Williams struggled with the officers, stabbing one with a plastic knife, although no injury was caused as the officer was wearing a stab vest.

When interviewed afterwards, he said: “If they had taken another five minutes I would have slit his throat.

“If I had killed him, I would’ve at least done something with my life - I would’ve achieved something.”

Williams admitted blackmail and making threats to kill at Blackfriars Crown Court and was jailed in February last year.

Cutting his sentence, Mr Justice Spencer - sitting with Lord Justice Gross and Mr Justice Stuart-Smith - said the crown court judge didn’t give him enough credit for admitting his guilt at his first court appearance.

Under the terms of his earlier imprisonment for public protection, Williams cannot be released from jail until the Parole Board considers he no longer poses a risk to the public.