The police use of cautions for adults in England and Wales is largely governed by a Home Office circular issued in 1994.
The Conservative government of the day was concerned about a glaring lack of national consistency in cautioning, and inappropriate use of cautions.
For example, in 1992, more than 1,700 people were cautioned for serious indictable offences, including attempted murder and rape.
The 1994 circular made it clear that this should not happen and laid down the criteria for the issuing of cautions.
There are two kinds of caution - formal and informal.
The informal one is an oral warning given by a police officer and does not count towards a criminal record.
A formal caution will normally be given at a police station by an officer of inspector rank or above. It is regarded as a serious matter and may be cited in any subsequent court proceedings.
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Often a victim will be contacted to establish the impact of the crime and their view of a caution.
A caution is not a conviction. But it is administered only in cases where there is sufficient evidence for a prosecution and where the subject has admitted guilt.
Before 1994, it was common for offenders to receive multiple cautions without any further action being taken.
Now, official advice is that only one caution - or in the case of juveniles, one reprimand or final warning - should be issued before follow-up action.
Before 2001, the caution, as part of a criminal record, had to be declared if raised at a job interview or in other circumstances. That is no longer the case.
Though the caution is issued by the police, it has often been done after consultation with the Crown Prosecution Service.
Under the 2003 Criminal Justice Act, a new conditional caution was introduced which enables CPS lawyers to attach certain requirements, such as attendance at a drug clinic or community reparation work.
George Mair, Professor of Criminal Justice at Liverpool John Moores University, who has done research on cautioning, said the police should now hand over all responsibility for cautions.
"I can't see the logic in having two systems running side by side. What is the rationale for the police retaining any right of punishment disposal?"
Do cautions work? Research carried out in 2002 indicated that the actual rate of reconviction of people cautioned for an indictable offence since 1995 was lower than the predicted rate.
This suggests that, in the main, it is an effective sanction.
In 2002, almost 143,000 cautions were issued for indictable offences in England and Wales. Only 1.2% of adult male sex offenders received a caution.