Nearly 5,000 registered sex offenders were monitored by police and social services in Scotland last year - the highest number since a new system for managing those convicted of such crimes was introduced eight years ago.

The figures have risen partly due to the high number of people now being convicted of internet-related offences such as downloading child abuse images and grooming.

Convictions have more than doubled in two years, from 252 to 527, according to a new report.

The authors are also calling on the Scottish Government to develop a strategy to combat 'sexting' which it says is putting young people at risk.

The in-depth review of the multi-agency public protection arrangements (Mappa) used to monitor sex offenders and attempt to prevent them from re-offending says they are working effectively and making a critical contribution to public protection.

The review carried out by the Care Inspectorate and Her Majesty’s Inspectorate of Constabulary in Scotland says that while the number of people subject to Mappa continues to increase steadily, there has been a decrease in the numbers deemed to pose the greatest threat to society.

While 4787 Registered Sex Offenders (RSOs) are being monitored this year, up from 4256 in 2014, only nine were deemed level three, or the highest risk, compared with 15 last year and 36 in 2013.

The report says that while 69 people were reconvicted of a serious crime of violence or indecency last year - the highest figure for four years, 98.2 per cent of RSOs commit no further such crimes. The most common reason for reconviction is failure to comply with conditions relating to checking in with the authorities.

The report says 'sexting', the practice of distributing indecent 'selfies' on social media or by mobile phones, has become a common phenomenon among young Scots.

It adds: "The scale of the problem could increase the vulnerability of young people at risk of exploitation and potentially result in them becoming subject of criminal justice processes."

It recommends that the Scottish Government should develop a sexting strategy to avoid the potential for young people to be exploited or end up with criminal records themselves.

Meanwhile the report says that police and social workers find it difficult to work out how much risk is posed by people convicted of internet offences and particularly whether they are likely to go on and attempt 'contact' offences, by meeting a young person they have groomed, for example.

It calls on the Scottish Government to give workers more guidance to help them saying staff find this challenging and lack the confidence to know who is a threat.

Fewer than one per cent of offenders monitored under Mappa are women, the report says, and the authorities monitored 15 under 18s last year, while 500 registered sex offenders (RSOs) were over 61.

The report says Police Scotland, Criminal Justice Social Work, Scottish Prison Service and NHS Boards who all have responsibilities for monitoring sex offenders work well together and carry out their duties effectively.

However, the review says the Scottish Government should engage more with the public to explain how Mappa keeps people safe while balancing the rights of the victim, communities and of offenders themselves.

Karen Reid, chief executive of the Care Inspectorate said: "This lengthy and detailed review provides evidence that MAPPA is effective and there are robust arrangements in place across the country to manage registered sex offenders.

“MAPPA has transformed partnership working between Responsible Authorities and relationships are particularly strong between Police Scotland and Criminal Justice Social Work Services.

“That said, we have outlined ten recommendations requiring a national response led by the Scottish Government in partnership with Responsible Authorities. We will now ask the Scottish Government and responsible authorities to create an action plan so that our recommendations are addressed.”

Andy Cowie Assistant HM Inspector of Constabulary in Scotland said: “We recognise that the challenges in managing registered sex offenders are often complex and that risk can never be eradicated.

“This is a demanding area in which to work and we were impressed by the commitment of all those involved in Mappa. The impact on them is recognised by their managers who provide quality support, advice and guidance."