HMP Wandsworth still does not have some of the "most basic security systems" in place following the alleged escape of a prisoner last year, the chief inspector of prisons has warned.
Charlie Taylor told BBC Radio 4's Today Programme the level of security at the prison was "unfathomable".
Daniel Khalife, 22, is alleged to have escaped the jail in September 2023.
On Wednesday, Mr Taylor issued an "urgent notification" about conditions at Wandsworth Prison.
It followed an inspection which found that England's second largest prison is stricken with severe overcrowding, vermin and rising violence among inmates.
Mr Taylor told the BBC: "I think the most worrying thing of all was despite the very high-profile alleged escape that took place last year... some of the most basic security systems simply weren't in place.
"Officers on the wing weren't able to account for their prisoners. They didn't know whether the prisoners were on the wing, in their cells or out at education or training," he said, describing the situation as "just unfathomable".
Mr Khalife allegedly escaped the prison in south-west London by strapping himself to the underside of a food delivery vehicle with bedsheets. He is due to go on trial in October.
'Such absolute despair'
Mr Taylor explained inspectors had found "very inexperienced staff [were] being led by very inexperienced staff, with a management team which had some very inexperienced managers in it.
"When that happens, some of the basic systems, some of that basic jail craft unfortunately goes by the wayside."
He added: "I don't think I've ever been to a place where I've come across prisoners in such absolute despair as we found at Wandsworth.
"There have been seven suicides at the prison just in the last year, which was extraordinary.
"The level of drugs in the prison was very, very high, you smelt cannabis everywhere you went around the wing."
The prison's governor, Katie Price, resigned during the inspection earlier this week.
An urgent notification requires the chief inspector of prisons to directly alert the justice secretary if there is an urgent and significant concern about the performance of a jail.
The secretary of state will then publish a response and a plan of action within 28 days.
After that, a long-term plan is established for continued improvement.
Mr Taylor's report is the latest official criticism of Wandsworth, following an inspection by its independent monitoring board last year.
The jail was described as "unsafe and inhumane" in the report, which said Wandsworth's failings reflected the wider prison system.
The report also found most prisoners were sharing cells designed for one person, and said inexperienced and burnt-out staff could not accurately account for all inmates during the day.
Prisons minister Edward Argar called Mr Taylor's report "deeply concerning" and said it showed the government needed "to go further still" in its support of HMP Wandsworth.
"In the coming weeks, we will be strengthening the management team with extra experienced staff to provide the leadership, culture change and training needed to turn Wandsworth around," he said.
"In the interim we are deploying more staff, including prison officers, to the prison and will set out further action shortly."
The chief inspector of prisons has issued six urgent notifications about prisons in England and Wales since November 2022.
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