Feltham Prison and Young Offender Institution has been labelled an "unacceptably violent place" by inspectors.
It was covered in gang graffiti and witnessed on average two fights or assaults every day, some of which were "very serious", HM Inspectorate of Prisons found.
Chief inspector of prisons Nick Hardwick said: "Feltham as a whole is an unacceptably violent place. Despite excellent work in some cases, staff were unable to prevent a high number of very concerning incidents that carried a significant risk of serious injury."
More top news
If you're dreading going to work Monday morning, how about this for a career change.
Police have released more images of people wanted in connection with what they describe as 'disorder' at a McDonalds in central London.
Four teenage girls, one of them aged 15, have been arrested following what police are describing as "disorder" at a McDonalds branch.