THE number of young offenders locked up in Scotland has more than halved since the SNP came to power.

In a dramatic consequence of falling youth crime, new figures show there are around 400 men and women aged 21 or under in the country's prison system.

That compares with a daily average of nearly 1000 youngsters on remand or on sentence in 2006-2007, the last full year of the old Labour-Liberal Democrat coalition at Holyrood.

Numbers have fallen so far that one of the main halls at the country's main facility for young offenders, Polmont, is now nearly empty.

Delighted prison leaders say the means they can now do more meaningful work to rehabilitate those inside

Scottish Prison Service spokesman Tom Fox said: "We are really pleased to see his dramatic reduction in the number of young people in our care. We hope numbers will reduce still further.

"This means that we have more time to do what we want to do, to provide those young people we do have with an opportunity to change."

There are currently 272 boys and men aged 16-21 serving sentences, many of them in Polmont Young Offenders Institution.

Another 112 are on remand, also mostly in Polmont. There are just 17 young women sentenced or on remand, most believed to be at Cornton Vale in Stirling.

Polmont until relatively recently operated close to its official capacity of 784.

Back in 2007, an official watchdog found that the facility was "dangerously overcrowded". The then HM Inspector of Prisons, Andrew McLellan, questioned whether all young offenders could continue to be kept there.

The Prison Reform Trust said Polmont was being used as a "dumping ground" for young people failed by the system.

The demographics of Scotland's jails are currently undergoing historic changes. The rise of historic sex cases means more and more elderly men are being jailed, with all the care problems that brings.

Overall crime is falling - but reports of sex offences continue to rise. The Herald understands there are now some 900 men in jail for sex offences. Such prisoners are now understood to take up an entire wing of Barlinnie.

As recently as 2012, the Scottish Prison Service was predicting that the country's jails would have more than 9000 inmates this year. The most recently figures, correct for April 24, show there are 7534. That compares with a maximum population of 8461 recorded in 2011-12.

Veteran police officer and anti-violence campaigner John Carnochan welcomed the decline in numbers at Polmont.

He said: "This is wonderful news. It shows that the drop in crime is not just reflected in recorded figures or in the number of young people being treated for violent injuries in our hospitals. It shows we are all on the right trajectory; police. young people, sociall workers and the judges who are sending fewer people to jail.

"It also means Polmont can now start to focus on rehabilitating the young people they do have.

"The prison service has all the skills needed to rehabilitate but wasn't able to do what it wanted when we were warehousing young people in jail.

"But we must keep our eye on the ball. The job is not done."

A study last year revealed that the peak age of offending had risen to 23, from 18 in the 1980s. The number of convictions for young men has fallen 70 per cent in a generation.