Calls for an inquiry into the state of jails in England and Wales have intensified after a prisoner died and two others were injured in a stabbing.
Jamal Mahmoud, a 21-year-old of Somali descent who had just become a father, was killed in the attack at HMP Pentonville on Tuesday and his family have hit out at the prison for "neglecting him".
The Prison Governors Association (PGA) claimed Government cuts to staff and resources meant the "tragedy" at the north London prison was "no massive surprise".
It follows a slew of warnings about safety behind bars, while Pentonville was last year singled out by former justice secretary Michael Gove as "the most dramatic example of failure" within the estate.
Mahmoud was jailed for six years and six months in July as one of two gang members sentenced after hiding a loaded Skorpion machine gun and ammunition in a garden in Enfield the previous July. He was already serving five-and-a-half years in prison for a separate robbery.
His sister Souzan, speaking on behalf of her mother Hawa, told ITV News: "For her to get a phone call that her son had died in prison is just devastating.
"I blame the prison more than the actual person that done it. They owed him a duty of care and they just neglected him.
"She's worried about my other brother who is also in prison."
Former prisoners described conditions as "horrible" and "disgusting".
Danny Rynne, a scaffolder from Enfield, north London, described Mr Mahmoud as "lovely" and "placid".
He said: "He's got a girlfriend who's just had a baby that was born two weeks ago. It's a shame what happened. I don't know too much about what it's about but it's a shock to everyone.
"He's a small fella and proper placid. He wouldn't say boo to no one unless somebody started on him."
Mr Rynne said he had just completed a stretch inside Pentonville himself, and called the jail " a horrible place, not good at all".
And Muneer Bhatt, 37, of Walthamstow, north east London, said he had just been released from a two-week stretch for breaching licence conditions for a car theft conviction.
He said: "They had the whole place locked down yesterday so nobody could get out of their cells. It's disgusting. It's a horrible place in there.
"After what happened yesterday, I'm going straight now. Pentonville is one of the most violent prisons in London."
Mr Bhatt and another source said the attack took place inside the G wing.
HMP Pentonville is a category B Victorian prison which opened in 1842 and holds more than 1,200 adult men.
An inspection report on the jail published last year said: "Most prisoners felt unsafe; levels of violence were much higher than in similar prisons and had almost doubled since the last inspection."
Plans to shut old Victorian jails have been outlined as part of a modernisation drive, with only HMP Holloway in north London confirmed as facing closure so far.
A Ministry of Justice spokeswoman said: "The Secretary of State has been clear that safety in prisons is fundamental to the proper functioning of our justice system and a vital part of our reform plans.
"We are fully committed to addressing the significant increase in violence, self-harm and self-inflicted deaths in our prisons."
Official figures show there were more than 20,000 assaults in prisons - 2,813 of them deemed "serious" - in the 12 months to December, a rise of 27% year on year, with nearly 5,000 attacks on staff - a jump of more than a third compared with 2014.
The data also showed there were six apparent killings, up from four in the same period in 2015 and the largest number for a year to March since current records started in 2000.
PGA national policy officer John Attard told the Press Association: "The Ministry of Justice (MoJ) statistics paint a very grim picture indeed.
"Sadly, it comes as no massive surprise to anybody close to this that we have had a tragedy such as this. The Prison Service paid staff to leave, the years of experience, the mentoring, the sharing of their experiences - a lot of that has been lost, and it is showing.
"It's why we need an inquiry into this."
The Prison Officers Association (POA) said it "once again" has serious concerns following the incident, and it warned " the unprecedented rise in violence in all of our prisons must not be under-estimated".
Police were called to Pentonville prison at around 3.30pm on Tuesday. Officers and paramedics found three inmates with stab wounds.
Two men, aged 21 and 30, were taken to an east London hospital, where they remain in a critical condition, a Metropolitan Police spokesman said.
Two men, aged 34 and 26, have been arrested in connection with the incident.
Islington South MP Emily Thornberry said the prison had been allowed to "deteriorate" and called on the Government to act.
She said: "It goes without saying that for a young man to be stabbed to death while in the custody of the state is unacceptable, whatever the circumstances, and my heart goes out to their family. But sadly, in Pentonville, it does not come as the shock that it should.
"It should not have taken a fatal stabbing to bring attention to these problems, and to highlight the fact that maintaining Pentonville in its present condition is simply not safe or sustainable."