THOUSANDS of prisoners are still being put behind bars for three months or less in Scotland despite a flagship law that was introduced to radically reduce short-term jail sentences.

Almost a third of sentences imposed by courts are for a matter of weeks, despite ministers freely admitting short-term stints in custody "don't work".

In 2010 Kenny MacAskill, who was then Justice Secretary, promised to end the "free bed-and-board culture" with controversial legislation which included a presumption against brief prison sentences which experts say increase risk of reoffending.

Sheriffs were told only to impose short sentences if there were compelling reasons for overriding the presumption.

However, in the first full year that the law was in force, 28 per cent of all offenders jailed received sentences of less than three months. The figure then rose in 2012-13, to 29 per cent and remained at the same level last year.

Prior to the act becoming law, 37 per cent of offenders were handed down prison terms of 12 weeks or under, although the figure had already been declining year on year and the trend halted once the legislation was introduced.

Hugh Henry, Labour's shadow justice secretary, said the Scottish Government must provide an explanation for the findings or face accusations the law-change had been about "grabbing headlines".

He added: "The SNP Government told us they were ending short jail sentences. They even passed a law on it, yet over 4,000 prisoners every year receive a short jail sentence.

"Nothing much has changed. SNP Ministers should be forced back to the Scottish Parliament to explain why they have abandoned their policy and are ignoring their own law.

"It was the SNP Government that made great play of this so Scots are due an explanation. Surely SNP Ministers have more important things to do make laws they have no intention of enforcing?"

It is understood that the Scottish Government is currently assessing the effectiveness of the 2010 Criminal Justice and Licensing Bill, as well as Community Payback Orders which were intended to replace short jail terms. A report is expected later this year.

The law, brought in by the minority SNP administration and passed only with the help of Liberal Democrat, Green and Independent MSPs, was strongly opposed by Labour and the Conservatives. Mr McAskill had watered down his original proposals, after originally supporting a presumption against six month sentences.

Juliet Lyon, Director of the Prison Reform Trust, said that short jail terms were a "waste of public money" and called on ministers to take action to ensure their position was enforced in courtrooms.

"[They] rarely achieve anything to address the causes of crime and often lead to the loss of homes, jobs and family contact - the things that reduce the risk of reoffending on release," he said.

"It is good that the Scottish Government is determined to reduce crime and prison numbers, now it needs to invest further in effective community sentences that command the confidence of the courts."

The law passed narrowly, with support of Liberal Democrats and Green MSPs, after SNP watered down its original proposals which originally included a presumption against sentences up to six months. Labour and the Tories voted against the legislation, which eventually passed by 64 votes to 61.

In 2013-14, 4,126 offenders were jailed for three months or less, from a total of 14,101 people who were given prison sentences. In 2010-11, 5,332 people were locked up for less than 12 weeks, with that total declining from 8,825 in 2006-07.

Margaret Mitchell, justice spokeswoman for the Scottish Conservatives, said: "Whilst the number of sentences of less than three months has decreased there is still and and always will be situations where a custodial sentence is the only option.

"Despite this the Scottish Government has not only failed but refuses to recognise the need to provide even the most basic rehabilitation for these prisoners. This in turn has resulted in the revolving door syndrome as these offenders continue to break the law on release."

Scottish Lib Dem leader Willie Rennie MSP said: "Liberal Democrats agree with the Government that short sentences don't work. But these figures show that the SNP Government's approach is not working either.

"Their rhetoric is fine but the reality is different with thousands receiving prison sentences that won't rehabilitate and wastes public money. There is still a revolving door in our prisons.

"The SNP Government has taken its eye off the ball on day to day services because of the referendum and now we are paying the price."

A spokeswoman for the Scottish Government said that judges had retained the discretion to hand out sentences of three months or less, if they believed it would be "more effective based on the evidence before them".

However, she added: "We know that short sentences don't work. They do nothing to rehabilitate the offender and all the evidence shows that it just leads to a revolving door to our prisons with individuals going in and out of prison only to reoffend time and time again. We believe a more effective approach is replacing these three month sentences with targeted work to address the underlying issues fuelling crime."