POLICE Scotland has activated the national Child Rescue Alert (CRA) system to help them trace missing three-year-old Mikaeel Kular.

The CRA system is a recent innovation in how British police forces manage the search for missing children. It's managed by the National Crime Agency and this is only the second time it has been triggered - the first being for April Jones in October 2012. It is rarely used because most cases of disappeared children involve an evidence trail that leads to an answer.

The CRA is a mechanism to centralise possible clues and leads from the public and sift these for information needed by the senior investigating officer in charge. An alert can be triggered by any British police force but only when a case matches three criteria: the subject must be under 18, there is a "reasonable belief" that the child is in imminent danger of serious harm and there is sufficient information for the public to be able to help the police investigation.

When someone calls the CRA national phone number - 0300 200 0200 - a dedicated operator at your local police force will answer. They will take down the information provided and check to see if it matches critical information provided by the inquiry's senior officer. If the caller says something that matches the keywords - for instance a reference to a particular car - the lead is immediately prioritised.

The information will be checked against information held elsewhere. In theory, this means the detectives will quickly receive the information they need without being deluged by thousands of calls.