The report said some foreign inmates could be waiting years to be deported
A quarter of prisoners in a Dorset jail are foreign nationals who despite completing their sentences have yet to be deported, a report has revealed.
Dorchester Prison was named in the final report of Dame Anne Owers, the Chief Inspector of Prisons.
Dame Anne raised concerns about the number of foreign inmates still in jail at the end of their sentences.
The Prison Reform Trust said the jail was designated for removing foreign nationals, explaining the high amount.
Dame Anne did report some improvements over her nine years monitoring prisons.
Figures released in Parliament revealed that last year about 550 foreign prisoners were kept beyond the end of their sentence in the average month.
Another 1,250 were held in immigration detention centres, and about a fifth were thought to have spent more than a year in custody after finishing their jail term.
Dame Anne, who is standing down, said: "We still find people who have been held in prison for a long time after sentence.
"On rare occasions it can be years, but it has certainly been improved.
"There has been a considerable focus on it and more prisoners being put into immigration detention."
The Prison Reform Trust said the policy was introduced without consultation.
Juliet Lyon, director of the trust, said: "Although the National Offender Management Service maintains that it will be able to provide better services if it holds foreign national prisoners altogether, few resources or training have been given to staff.
"We expect the prison service authorities to monitor the impact of this policy to make sure that foreign national prisoners are treated properly."
Each inmate costs an average of about £38,000 a year to be kept in prison.
Dame Anne also reported that jails in England and Wales could become more unstable because of budget cuts and a rising population.
Prisons have been told to save 3% this year from their budgets while the population continues to grow by about 2,000 a year.