Blantyre House is no longer “the jewel in the prison service crown.”

That was how it was described by Nick Hardwick, the Chief Inspector of Prisons, at its last inspection in 2010, but an unannounced inspection in September found that standards had slipped.

His report published yesterday still found the unit “had many strengths”, but it needed to adjust to its changed population.

The semi-open prison holds prisoners who are coming to the end of their sentences and are being prepared for release.

At the time of the last inspection, it was able to select the prisoners it took and to tailor its services to their needs.

Now allocations are made by a central unit and Blantyre House can no longer pick its inmates.

Inspectors said that as a consequence the prison was holding men who presented a wider range of needs and risks than before, but its work and resources had not been sufficiently adjusted.

The primary purpose of the prison was resettlement, but there were too few places available for paid or unpaid work in the community and efforts to assist prisoners in finding something were “lacklustre.”

There had been two serious assaults, in part due to the availability of ‘spice’ – a synthetic cannabis-like drug – in the prison.

In a survey, 36% of its 121 prisoners said it was easy to get illegal drugs, up from 20% in 2010.

Inspectors found there was very little self-harm by prisoners, but there had been a suicide, the first ever at the prison. However, despite these shortcomings, the inspectors found that most prisoners still had a safe and productive experience at Blantyre.

The scheme of release on temporary licence was considered to work well. Only three prisoners had failed to return in the past 12 months, but all had been quickly recaptured.

Michael Spurr, chief executive of the National Offender Management Service (NOMS), said: “We recognise that the population at Blantyre House is more complex and challenging than previously and the Governor and his team will have the support needed to take forward the recommendations in the report.”