The standards and safety at HMP Onley are in decline, a new report has claimed after a surprise inspection in summer this year.
Assaults in the prison, which holds around 740 prisoners mainly from London, was found to have tripled since the last inspection in 2012.
Inspectors also found drug reduction strategies were lacking, staff shortages meant prisoners could not attend activities and training sessions as often as they should, and offender supervisors had little contact with prisoners.
Good aspects of the prison were also uncovered by the inspection, which included the strong staff-prisoner relationships, the education and training opportunities along with the support for prisoners settling back into the community.
Chief inspector of prisons Peter Clarke said: “The challenge for Onley is to find ways to halt the decline, and there are clear lessons to be learned.
“There was a clear need for the leadership of the prison to get a grip of the problems facing them and move away from merely reacting to events.
“Staff shortages have had an impact on many areas of service delivery, but they did not offer an excuse for a decline in standards.
“There was actually much good work being done at Onley.”