Police are to be given new powers to store the DNA of Scots children who commit violent and sexual offences as part of a crackdown on youth crime.

Currently, the genetic profiles of young offenders whose cases are dealt with by a children’s hearing are destroyed, even if they admit the crime or the case against them is proven.

However, ministers want to change the rules to allow DNA samples to be held for three years in order to identify under-16s who go on to commit further offences.

An estimated 2,000 to 3,000 children per year are expected to have their DNA and fingerprints retained as a result of the changes.

The new rules will apply to children who have committed sexual and violent crimes, as well as so-called “trigger” offences, such as fireraising, which indicate a propensity to violence.

The change in the law is recommended in a new report commissioned by justice minister Kenny MacAskill and is seen as more proportionate than the policy in England, where DNA can be taken from children who have been arrested and stored indefinitely, even if they are never convicted.

Ministers have already ruled out such a blanket approach in Scotland and believe that the three-year period is sufficient to cover the time during which youngsters are most likely to reoffend.

But the idea has alarmed some human rights campaigners. Shami Chakrabarti, director of civil rights group Liberty, said: “This is picking on the most defenceless and under-represented group in society. It’s an authoritarian experiment on people who can’t fight back.”

Margaret Smith, the Scottish Liberal Democrat justice spokeswoman, added: “We need to be very clear about the category of offence involved. Even something on the face of it that sounds serious, like a sexual offence, could be two teenagers going before a panel for consensual sex.”

The government will launch a public consultation on the proposed changes next month.

A government source said: “There are about 60,000 children referred to hearings each year, most because of welfare problems. Only a small number of these would be sampled for DNA and fingerprints because of the violent or sexual nature of their offending, around 2,000 or 3,000 a year.

“In England and Wales, DNA from any child who’s arrested can be put on a database regardless of whether there is a conviction. In Scotland it is proposed that retention of children’s DNA should only happen for certain categories of serious offence, and only where the child has been through a hearing and admitted or been shown to have committed an offence. Children will be treated fairly, but equally the public are getting protected.”

The report, by Professor James Fraser, head of Strathclyde University’s Centre for Forensic Science, also recommends allowing police to hold for three years the DNA and fingerprints of adults charged with sexual and violent offences but not convicted. Currently, only the DNA can be retained.

Earlier this week, Scotland’s most senior police officer floated the idea of taking DNA from every Scot in order to build up a permanent database on the entire population. Stephen House, chief constable of Strathclyde Police, suggested that Scotland should copy England and retain the DNA of suspects as well as convicted criminals.

About 4.2m DNA profiles are currently stored on the English database, which is the largest of its kind in the world, but about 1m of these are from people who have not been convicted of a crime.

The Scottish database holds around 200,000 profiles, and only DNA from convicted criminals is held permanently.

Dr Helen Wallace, director of GeneWatch, said the proposed figure of up to 3,000 children a year was “quite high”, and warned there was a danger children could be stigmatised by the process. However, she said retention for three years seemed fair.

John Scott, the Scottish human rights lawyer, also said three years was “a reasonable compromise” and markedly better than the English system.

A Scottish government spokesman said that ministers will issue a formal response to Fraser’s report “in due course”.

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