The First Minister has been urged to carry out a review of the flagship community payback order (CPO) scheme after it was confirmed 7% of those sentenced for rape or attempted rape are not given prison terms.

Tory leader Ruth Davidson insisted action "is so obviously needed" after it was reported six CPOs were issued for the rape or attempted rape of adults in 2014-15.

Ms Davidson described the scheme, which started in 2011, as "one of this government's key justice policies" as she told Nicola Sturgeon the orders were being given to those convicted of crimes such as "sexual assaults against children and rape and child rape".

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The First Minister said rape was "one of the most heinous offences that can be committed in our society" as she said statistics showed "the vast majority, the overwhelming majority of rape cases, 93% of rape cases, incur a custodial sentence".

Ms Davidson, who pressed her on the issue at First Minister's Questions, said: "That leaves 7% that don't.

"The trouble is too often the response from ministers is simply to declare that the system is working fine and everyone should just accept it.

"But CPOs aren't working fine. They were an SNP creation and they are this government's policy, but we have learned today they are being applied to serious crimes like rape when they shouldn't be, up to a third of them are breached and up to a fifth of them don't contain any punishment element at all.

"I believe we now need a calm, considered fresh review by the Scottish Government on the way that CPOs are handed out."

Ms Sturgeon rejected Ms Davidson's call, stating: "There was an independent evaluation published in 2015 of CPOs that showed that they are viewed with a degree of confidence by most sheriffs and are seen as an improvement on previous community sentences."

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She added: "It is also the case that those given a CPO are less likely to re-offend and be reconvicted."

When ministers brought in CPOs, the aim of the scheme was "to ensure that offenders pay back to society and to particular communities" by requiring them "to make reparation, often in the form of unpaid work", and also by helping them to "address and change their offending behaviours, thereby improving the safety of local communities".

Ms Davidson said: "Every year we discover nearly a third of orders are broken with scant evidence that people are punished."

She also said that about one in five CPOs "are handed out without any work requirement placed on criminals who receive them".

The Tory leader said: "We absolutely accept the need for community sentencing but what is the First Minister doing to address these issues with CPOs?"

Ms Sturgeon agreed that cases of rape and other sexual offences "should be treated with the utmost seriousness and severity".

The First Minister added: "Indeed, the average length of custodial sentences for rape and attempted rape are now 17% longer than they were back in the year 2006-07. I think all of that is right and proper.

"Custodial sentences are passed down in rape cases in a higher percentage of cases than for almost all other offences.

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"The average length of custodial sentences is now longer, we are seeing more successful prosecutions for rape and attempted rape, 125 convictions in 2014-15, which is up from 89 in the year before that."

She stressed sentencing in individual criminal cases is a "matter for the courts and it would be wrong for me as First Minister to comment on any individual case".

She added: "We must trust the independent judiciary to make the decisions they deem appropriate in individual cases.

"It would be absolutely wrong - and I suspect Ruth Davidson would be one of the first to say it was wrong - if I as First Minister started to pass comment on individual sentences passed down by judges."

She also told MSPs that criminals given a CPO are subject to "robust and ongoing" monitoring and assessment, with courts entitled to impose jail terms on those who breach their orders.

In 2014-15, 17% of CPOs were revoked because they had been breached in some way, she added.

Ms Sturgeon continued: "Individuals who are released from a custodial sentence of six months or less are re-convicted more than twice as often as those who are given a community payback order.

"Now what that tells us is that non custodial sentences like CPOs, when they are handed down in appropriate circumstances, are more effective than short-term prison sentences in reducing re-offending.

"Where it is appropriate - and I absolutely stress where it is appropriate - keeping people out of prison in general terms and helping to rehabilitate them in the community so they are less likely to re-offend is in general terms a good thing.

"None of that takes away from the seriousness of certain types of offences which should always be treated with the utmost seriousness by the courts."