HMP Portland 'not learning from deaths' inspectors say
Recommendations made after the deaths of inmates at a prison and young offender institution in Dorset have not been fully implemented, inspectors have said.
An unannounced inspection at HMP Portland said "greater attention" needed to be paid to investigations into self-inflicted deaths.
It also raised concerns over substance misuse and accommodation standards.
The National Offender Management Service said changes were being made.
There have been three self-inflicted deaths among inmates since 2009, including Jordan Buckton, 20, who was found hanged in his cell at the institution in February 2012.
Inspectors from Her Majesty's Inspectorate of Prisons said there were still "weaknesses" in the organisation of care for prisoners in crisis.
They were concerned to find support for prisoners with substance misuse issues had worsened, partly because of staff shortages.
Their report criticised provision of education, training and employment for inmates and said the prison faced "operational challenges" over the age profile of prisoners and the pressures of overcrowding.
A previous report in 2012 found there had been a rise in violence and "limited progress" in tackling self-harm.
Chief inspector of prisons Nick Hardwick said: "This is a mixed report and contains significant criticisms under all of our healthy prison assessments.
"Learning from investigations into deaths in custody certainly required greater attention and the lack of meaningful activity was a real concern."
However, he said there was "evidence of some progress."
Inspectors said the prison was fundamentally safe, use of force was not excessive and relationships between staff and prisoners were reasonable.
Michael Spurr, chief executive officer of the National Offender Management Service, said: "Reducing self-harm and self-inflicted deaths remains a top priority for the service and we continue to work very closely with the Prisons and Probation Ombudsman, who investigate all deaths in custody, to ensure we can learn from their recommendations and try to prevent deaths and self-harm wherever possible."
He said extra staff had been recruited to improve levels of "purposeful activity".