Healthcare standards at a prison that opened a £15m hospital wing earlier this year have been condemned by the Chief Inspector of Prisons.
Anne Owers said "excellent" facilities at Pentonville jail in north-east London were let down by a lack of safe and effective primary care.
The report identified clinical supervision of nurses as "non-existent" and "unsafe" drug dispensing practices.
It was released after an inspection of the 1,150-inmate jail.
Ms Owers said: "In almost all the areas we inspected, systems and management structures were simply inadequate to ensure agreed policies were being implemented safely, decently or consistently.
"It illustrates only too well the problems facing overcrowded local prisons and the consequences if they are not actively addressed."
On some wings, prisoners were locked up for 22 hours a day, while other areas were dirty and infested with mice, cockroaches and pigeons, the report said.
Prison Service director general Phil Wheatley said: "To successfully operate a busy London local prison in these circumstances is an exceptionally difficult management task, and requires an experienced and skilful governor.
"The new governor and his team will ensure Pentonville moves forward and I am confident this will happen."
The healthcare centre opened in January, just weeks before the inspection team's visit.
Prison governor Gary Deighton said: "It had been opened in a rush and that showed.
"It could be an excellent facility and when we get it properly functioning, it will be."
Problems with pest infestation were being addressed, he said.