Gloucester Prison has been criticised for overcrowding and a lack of provisions available for inmates.
The prison houses more than 300 inmates
In a new report, the Independent Monitoring Board for the prison says conditions at the Victorian-built jail are not good enough.
The Prison Service defended the way the jail is run.
It said that while the building was old, the service's performance demonstrated what can be achieved in less than ideal circumstances.
Mary Robinson, chair of the inspection board for HM Gloucester Prison, said: "I think some members of the public would be shocked to know the prisoners live in a small cell, two of them, with a toilet and have to eat their meals there."
The report highlights problems which it says need to be addressed including overcrowding, which hinders efforts to rehabilitate prisoners, poor dining provision and cramped cells.