It is intended as a common-sense move to save young teenagers who have consensual sex from being prosecuted.

But the recommendation by the Scottish Law Commission to effectively "decriminalise" sex between children aged 13 to 15 has divided opinion and provoked claims that it could send out the wrong message and leave vulnerable youngsters at risk.

The commission's recommendation, put out to consultation in December on behalf of the Scottish Government, is that those aged 13 to 15 who have consensual sex with one another should not be criminally liable, a change from the current situation in which a boy of that age could be prosecuted for having consensual sex with a girl of the same age.

The commission stated in its report that "many older children may have the capacity to consent to sexual activity", adding: "It seems to be an extreme outcome that 14 or 15-year-old children are to be prosecuted for engaging in activities that are both consensual and, as a matter of empirical fact, prevalent."

The age below which no form of sexual activity is regarded as appropriate, 13, would remain unchanged and sex between adults and those under 16 would remain a criminal offence.

The move is part of a review to tackle a "lack of coherence" in existing law, in which some offences only apply in respect of male offenders and female victims or male offenders and male victims.

It also comes at a time of societal change, when the onset of puberty is becoming earlier. Girls are reaching puberty 18 months before their mothers did, and almost two years earlier than their grandmothers, according to research published two years ago by the psychologist Dr Aric Sigman.

The response to the proposed change has been generally positive, but concerns have been raised about the vulnerability of apparently consenting young teenagers and also on how the change might fit in with ongoing attempts to tackle Scotland's teenage pregnancy rates, which remain among the highest in Europe.

Sexually transmitted infections among teenagers generally have also increased in recent years.

One of the thorniest issues the government must face, should it proceed with the move, is how it will be perceived publicly. As the debate over cannabis shows, moves to decriminalise are often taken as symbolic.

Only four years after it was reclassified from class B to class C, the UK Government is pushing for cannabis to be returned to class B, to send out a strong message about its dangers.

There are already signs that a move to decriminalise sex between 13 to 15-year-olds might be seen as effectively lowering the age of consent. The Association of Chief Police Officers in Scotland believes so and is opposing it on those grounds.

Victim Support Scotland, which generally supported the recommendation, raised a further anxiety, namely "whether a child can give meaningful consent".

The commission stated that it recognised concerns about the validity of consent, especially in cases where one party is older and more experienced than the other and said: "There will be cases where there are issues about the welfare of children who are sexually active and who should be referred to a children's hearing."

For this reason, it recommends the creation of a new ground of referral to a children's hearing.