Noranside prison, near Forfar, which currently has about 100 prisoners, will be mothballed for a week. Any inmates not eligible for release will be moved to nearby Castle Huntly.

A Scottish Prison Service spokesman said today: “That’s the plan at the moment. We did that last year. The numbers in the open estate are quite low, but if you have prisoners in the open estate and they’ve been risk assessed, it makes sense that gets tested.

“That’s part of the parole process. If the prisoners misbehave or breach their conditions they’re back in closed conditions.”

Noranside and Castle Huntly have a combined capacity of about 500. The larger Castle Huntly, near Dundee, would be able to accommodate the reduced open population over the festive period on its own. Serious offenders, including killers, could be among those released.

The SPS spokesman said that no final decision had been taken on the numbers to be allowed home on leave at Christmas.

But Tory community safety spokesman John Lamont branded the plans quite incredible.

He said: “Many victims of these criminals, and families of those killed, are still bearing emotional or physical scars and they will have to watch in horror as they are sent home to enjoy a week with their families.

“Where is the justice in that? What will Alex Salmond say to anyone who becomes a victim if any of these inmates commits a crime whilst let loose for Christmas?

“It is all part of the SNP’s agenda to empty our prisons, whatever the cost.”

The open estate has been at the centre of political rows in recent years.

Sex offender Robert Foye absconded from Castle Huntly in 2007 after being let out to attend an Alcoholics Anonymous meeting and raped a 16-year-old girl before being recaptured.

This led to a tightening of controls over who is sent to open jails.

But this year murderer John Brown and armed robber Brian Martin - dubbed The Hawk - both absconded in quick succession from Castle Huntly.