The Independent Monitoring Board (IMB) has praised the staff at Erlestoke Prison near Devizes but remains concerned at the number of prisoners who remain there beyond their tariff date.

For the third successive year the IMB’s annual report said prisoners who remain in prison after they were due to be released has a destabilising influence on the prison.

The report says: “We remain particularly dissatisfied with the Government’s plans for existing sentenced Indeterminate Public Protection and Indeterminate Sentence Offenders offenders being held, often for many years, in excess of their tariff.”

It said one prisoner was held at the prison on a four month tariff and was still in custody after four years.

More than half of the inmates at Erlestoke, which has a capacity of 494, have indeterminate sentences.

Andy Rogers, governor of Erlestoke Prison, said: “Erlestoke is a national resource and focuses on housing long term offenders. Over half of the population are serving indeterminate sentences with no end dates of their sentence attached to them. These include offenders who need to prove to the Parole Board that their individual risks have reduced to levels where they are safe to be released into the community without high risk of reoffending or causing future victims.

“In some circumstances this means that some offenders who have been given reasonably short sentences initially are thought to be at risk of further offending because of numerous reasons including patterns of their offending and the risks associated with that. In these circumstances they may well be retained in custody until the risks are reduced and sometimes this can run beyond a 'tariff' date. The decision on sentencing and release is made by the judge in the individual case and the Parole Board and is not something that as governor I am able to control or influence.”

The IMB’s report covers the year up to March 31 2014 during which time the prison was the best performing C prison in the south west.

The IMB’s report says: “The governor, management and staff continue to work extremely hard and successfully in providing a safe and secure prison despite considerable budgetary and resource constraints. The safe environment was specifically highlighted in an excellent unannounced inspection carried out towards the end of 2013 by Her Majesty’s Inspector of Prisons.”

The IMB was impressed with the range of purposeful activity provided by the prison for inmates but was concerned that art and drama are no longer provided through an offender learning and skills service contract.

In last year’s report the IMB thought the amount of money spent on each prisoner for three meals a day, at £1.94, was inadequate. During the past year the budget was £2.03 per offender, which Mr Rogers said had risen in recognition of increased food costs.