Jamie McIvor BBC Scotland's Politics Show reporter

A motorist heading from Perth to Dundee could mistake Castle Huntly for yet another local landmark.

The appearance of Castle Huntly can be deceiving

The 15th Century castle stands about a mile south of Longforgan - and from the distance a stranger might easily wonder if it was a tourist attraction.

Critics of open prisons would raise a wry smile at that suggestion. Open prisons have been condemned by some - including Scottish Conservative justice spokesman Bill Aitken - as "holiday camps".

Since the first open prisons were established half a century ago, they have had their critics but now they are under scrutiny as never before.

The challenge for the Scottish Prison Service (SPS) is to prove to a sceptical public that open prisons are a vital and well-run part of the system, which deserves their confidence.

It insists the jails are anything but a soft option.

Instead the service is proud of the important part it plays in the rehabilitation process for inmates coming towards the end of their sentence.

Recently, the name of Castle Huntly has almost become a joke for critics.

Prisoner trust

Recent concern about the number of prisoners absconding intensified after the case of Robert Foye, convicted for attempted murder.

Foye absconded from Castle Huntly and raped a teenager while he was on the run.

He is one of a total of 140 inmates to abscond from Scotland's two open prisons in the past two years.

The SPS is keen to tell its side of the story.

To show people what an open prison is really like. Ian Whitehead, the governor of both open prisons, took me on a tour of Castle Huntly.

There is no external wall - not even a perimeter fence. Homes lie just yards from the edge of the prison grounds. Entering the prison grounds seems no harder than entering a hospital.

But security is still present, with the complex covered by a CCTV network.

The accommodation has modern facilities

The ethos of the prison is to show the prisoners some trust. If they abuse that trust, they will be punished or sent back to a normal "closed" jail.

Mr Whitehead spoke with pride about the prison's achievements - but was quick to acknowledge that the number of prisoners absconding was far higher than he would like.

He believes two facts place the raw figures in context.

Firstly, the number of inmates at open prisons has risen substantially in recent years and, with that rise, has come more opportunities for prisoners to abscond.

That means, he claims, that the proportion of prisoners who abscond has actually fallen.

Secondly, the vast majority of prisoners go missing when they fail to return from authorised trips to the outside world.

Few "escape" by walking out of the prison grounds.

Life changes

Showing me around, Mr Whitehead is clearly proud of the work of his staff and the achievements of some of the inmates. Some spend the day working around the prison.

Others are sent on placements with organisations in Tayside.

The whole aim is to help break prisoners back into the outside world, to give them personal confidence and the skills to get a job after their release.

Educational opportunities are on offer. Posters advertise Spanish classes or courses in IT skills. Sport is encouraged and there is also help for prisoners overcoming addiction.

Some prisoners are lucky enough to live in comfortable new accommodation. A typical room is shared by two inmates - and might have washing facilities and a portable TV.

In some ways, the accommodation block is not unlike a student hall of residence - but with some major differences.

Inmates are not normally locked in their rooms - but they can be locked in by prison officers if necessary and the officers can always gain access.

And from nine o'clock at night until seven o'clock in the morning, the doors at the end of residential corridors are locked.

Important questions are being asked about open prisons.

Chief Inspector of Prisons, Andrew McLellan, fears overcrowding in other jails may lead to prisoners being sent to open jails before they should be - something Mr Whitehead insists does not happen.