Large amounts of rubbish outside Winchester Prison led to a jail rat infestation, a report found.
Between June 2014 and May 2015, the Independent Monitoring Board (IMB) said the prison was under “considerable external pressures”.
It also said there was increased use of so-called legal highs and violent behaviour.
A rat infestation had “caused problems inside and outside, including the destruction of CCTV cabling”.
Prisoners were throwing rubbish out of their cell windows, allowing it to collect in outside areas, the report said.
“This year there has been a rat infestation, perhaps as a consequence, which made working conditions in control, located in part of the oldest building, almost unbearable,” it added.
The report also stated “many prisoners spend their time in the workshops spinning out what little work there is or simply sitting chatting”.