A leading sheriff yesterday said Scottish courts could no longer guarantee public protection after attacking a "nameless official" over the early release of a youth who committed further crimes while on a home curfew order.

Sheriff Robert Dickson, who is president of the Sheriff's Association in Scotland, said Jason Jarvie, 20, had been freed to reoffend because an official had ignored a judicial decision.

Jarvie, who had a history of breaching tagging orders and offending while on bail, was freed after serving less than a third of a 15-month sentence at Polmont Young Offenders' Institution, near Falkirk, which is run by the Scottish Prison Service (SPS).

The "nameless official" was not identified. However, decisions about whether or not to release a prisoner on Home Detention Curfews (HDC) are made by the governor or a designated unit manager. The governor of Polmont YOI is Derek McGill.

Courts are responsible for sentencing. But a unit within the SPS assesses whether certain people are suitable for HDCs. There are exemptions such as sex offenders.

Opposition politicians called on Justice Secretary Kenny MacAskill to order an investigation into the case.

Sheriff Dickson's criticisms came three months after Mr MacAskill accused Labour of "playing games" by forming an alliance with the Tories to block plans to extend home tagging as a way of cutting Scotland's record prison population. Proposals for the system will now go to a full vote at Holyrood.

Jarvie was ordered to be detained in March 2007 following a series of crimes including violence, dishonesty, public disorder, failure to attend court, drugs misuse and committing offences on bail.

Yesterday Airdrie Sheriff Court heard that he pleaded guilty to causing malicious damage to a house in Airdrie, North Lanarkshire, on October 1, last year while on probation and under a home curfew order. Jarvie, from Coatbridge, threw paint on to the house's front windows and the garden path, scrawling the words "grass" and "young mob". The residents were asleep.

Sitting at the court, Sheriff Dickson said it could have come as "little surprise to anybody" that he had reoffended after his release last August given his previous behaviour.

Sheriff Dickson went on: "At a time when society was entitled to expect that the court's 15-month sentence would allow some respite from your repeated criminal activities, when you should have been incarcerated and innocent homeowners should have been protected from your mindless behaviour, some nameless official has chosen to ignore a judicial decision, to turn an apparent blind eye to your past record of ignoring curfews and to allow you the freedom to damage the property of somebody you did not know."

He added: "There can be no doubt that had you remained in the young offenders' institution for the time selected by the sheriff, this crime could not have been committed.

"I and every other sheriff can no longer give any assurance to the public that they are going to be protected for any particular period if our decisions can be overruled by a person who has neither heard the facts of the case nor had any input to the judicial decision to select a particular length of custody."

Scottish Tory justice spokesman Bill Aitken said the case showed we are living in "soft-touch Scotland" and praised Sheriff Dickson.

Mr Aitken added: "By acting in this manner the Scottish Prison Service is overriding a judicial decision which is quite intolerable."

Labour and the LibDems called on the justice secretary to order an urgent investigation into the case.

A Scottish Government spokesman said: "Scottish ministers can neither comment on, nor intervene in, the sentences imposed in individual cases."

Sheriff Dickson deferred sentence on Jarvie until July 9 to allow a new probation report to be prepared.

Jarvie was released on bail with the condition that he must remain at his bail address from 6pm to 6am.

Sheriff's statement Before deferring sentence, Sheriff Dickson made the following statement: "On 14th March 2007 you were sentenced in this court to a total of 15 months detention in relation to a series of crimes including violence, dishonesty, public disorder, failure to attend court, drugs misuse and committing offences on bail. Your record shows that on previous occasions courts have tried to curb your criminal activities by making restriction of liberty orders; you have repeatedly breached them.

"Notwithstanding the sheriff's sentence of 15 months, you were allowed out after 41/2 months on 3rd August 2007 on a home curfew order. In view of your past disregard for a requirement that you remain within a house, it can have come as little surprise to anybody that you defied this order also.

"At a time when society was entitled to expect that the court's 15 month sentence would allow some respite from your repeated criminal activities, when you should have been incarcerated and innocent homeowners should have been protected from your mindless behaviour, some nameless official has chosen to ignore a judicial decision, to turn an apparent blind eye to your past record of ignoring curfews and to allow you the freedom to damage the property of somebody you did not know.

"There can be no doubt that had you remained in the young offenders' Institution for the time selected by the Sheriff, this crime could not have been committed.

"I and every other Sheriff can no longer give any assurance to the public that they are going to be protected for any particular period if our decisions can be overruled by a person who has neither heard the facts of the case nor had any input to the judicial decision to select a particular length of custody."