A new smoking ban, psychoactive drugs and influx of younger prisoners have fuelled an increase in violence at a jail, prison bosses say.
The problems come despite some improvements at the overcrowded HMP Leicester, according to inspectors.
At the time of an unannounced visit by the prisons watchdog the jail had 308 inmates - about 100 more than it was designed for.
The prison service said it would "continue to prioritise safety".
Since a 2015 report declared the prison unsafe, violence had stabilised or decreased in 2016, but rose dramatically last summer before a further surge in November, the report found.
'Threat to stability'
HM Inspectorate of Prisons said: "Managers attributed this rise to a combination of the smoking ban, an influx of younger prisoners from HMP Glen Parva and the influence of new psychoactive drugs."
While "drugs and psychoactive substances remained a threat to the stability of the prison" there was evidence the jail was trying to address this, it added.
Peter Clarke, HM Chief Inspector of Prisons, said: "In 2015, we reported on a prison we considered unsafe.
"It remained the case that Leicester was still not safe enough, but it is right to acknowledge that the governor and his staff were showing considerable determination in trying to make the situation better.
"The theme of this inspection, and the word we repeatedly return to, is improvement."
Other concerns at HMP Leicester:
- Use of force and use of special accommodation had increased considerably
- Illicit drugs were easily accessible
- Poor living conditions. Communal areas were grubby and most showers were still waiting to be refurbished. Some cells were cold and some were not equipped well enough, including a lack of screening for the in-cell toilet
- Cells designed for one should not hold two prisoners
- Three self-inflicted deaths since the last inspection. Although self-harm had reduced, it was higher than at similar prisons. However, work was being done to improve this
Good practice at HMP Leicester:
- Additional welfare checks were carried out routinely during prisoners' first 24 hours in custody
- A comprehensive database had been developed to analyse violence locally, rather than relying on central systems
- Excellent range of creative activities to support personal development and rehabilitation
- The visiting area had been refurbished to a high standard
- Prisoners had access to an unusually well-integrated and responsive pathway of care
After the inspection in 2015, 70 recommendations were made. The prison had achieved 31 of those, partially achieved eight and not achieved 29. Two were no longer relevant.
Prison Service chief Michael Spurr said: "Significant work has been done to improve safety and conditions at HMP Leicester and I'm pleased that the progress made has been highlighted in this report.
"The prison will continue to prioritise safety but will also seek to improve education and employment outcomes in line with the new strategy launched by the Secretary of State for Justice last week."
Andy Baxter, from the Prisons Officers' Association, said overall levels of assault and self inflicted death remained a concern for the association.
Talking about the improvements, he added they were "a direct result of a governor and the senior management team working hand-in-hand with staff representatives within the establishment".