An unannounced inspection of a prison for foreign national men found "chaotic and tardy" Home Office processes delayed the release of foreign prisoners.
Inspectors found HMP Huntercombe, near Henley-on-Thames, Oxfordshire, to be" safe and respectful" but release planning was "not sufficiently good".
The prison has housed foreign nationals since 2012.
A UK government spokesperson said it was "taking decisive action".
Inspectors visited HMP Huntercombe in August, to follow up from their last visit in 2017.
The report concludes that prisoners were kept safe and violence figures "remained low compared to similar establishments and most incidents were not serious".
It also said they were "treated with respect" from "polite and friendly" staff.
However, the report said that those high scores were "often undermined because of chaotic and tardy Home Office processes" in processing cases of prisoners eligible for early removal.
"Although there was a team of Home Office staff in the jail... long backlogs in central decision making meant that prisoners continued to be left anxious and confused," the report said.
The education and training provision was not good enough, and staffing issues meant classes were often cancelled.
But it also added that a stoicism course supported prisoners to better manage negative and unhelpful emotions and behaviour.
"The Ministry of Justice (MOJ) should clarify the role of... offender management and resettlement in foreign national prisons to ensure that the needs of prisoners, including the risks they pose, are addressed before they are released or removed," the report recommended.
HM Chief Inspector of Prisons Charlie Taylor said that HMP Huntercombe "continues to be one of the best prisons in the country".
"I expect progress to continue if the education provider radically improves and if a small minority of officers become more professional and engaged with their role," he added.
A government spokesperson said: "This report rightly praises the safety of the prison, healthcare services and the prison's strong leadership.
"We are taking decisive action to address the issues raised, including improving education provision and building positive relationships between staff and offenders, for example through cross-cultural events.
"We also remain committed to ensuring foreign criminals' cases are swiftly resolved and where appropriate they are deported to their home country at the earliest opportunity."