Chronic staff shortages, food running out and a surge in violence were among the findings of a critical prison report into Wormwood Scrubs.
Inspectors also found areas of the west London jail were strewn with litter, attracting rats and cockroaches - writes bbc.com
Chief inspector of prisons Peter Clarke said the findings painted an "extremely concerning picture".
The Ministry of Justice (MoJ) said the jail was recruiting staff in a bid to "urgently" raise standards.
Wormwood Scrubs 'dangerous for officers'
The HM Inspectorate of Prisons' report said Wormwood Scrubs, which holds more than 1,200 men, had high levels of often serious violence, resulting in some significant injuries.
It also detailed how food routinely ran out in one wing, with staff having to source a half-used tray from another servery or distribute "mountain survival" dried food packs.