Chelmsford Prison is violent, unsafe, overcrowded and a hotspot for drug smuggling, according to inspectors.
A report from HM Inspectorate of Prisons has revealed that £15,000 of contraband - including drugs, phones and packages thrown over the wall - was found in the prison in a single month.
It said large volumes of drugs were smuggled in by the many organised crime gang members in the Essex jail.
It also found there had been 16 suicides there in just eight years.
Levels of violence were “far too high” and not enough had been done to ensure the underlying causes were understood or addressed. Use of force by staff was also high.
Much of the violence was related to the supply and use of illicit drugs, and the positive drug testing rate was among the highest inspectors had seen at more than 40%.
Inspectors found that Chelmsford was heavily overcrowded, particularly in the older blocks dating back to the 1830s.
The prison was also poor in providing prisoners with purposeful activity, including training and education, with “severely restricted” time out of cell for many prisoners. The majority of staff were inexperienced.
Peter Clarke, HM Chief Inspector of Prisons, said he seriously considered invoking the Urgent Notification (UN) protocol.
This publicly requires the Secretary of State for Justice to take urgent action to tackle significant problems in a jail and has been invoked four times since the protocol was ratified in November 2017.
However, Mr Clarke said an improvement plan was in place and the acting governor "enjoyed the confidence and support of her staff".