Empowered to use alternatives to juvenile court referral in dealing with young offenders, the British police in general, and the London Metropolitan police in particular, have been increasingly choosing official warnings in the presence of parents or guardians in preference to other diversions (e.g., referral to youth protection services. Such official warnings by the police become a matter of public record, being filed with the Home Office and school authorities. While it is generally acknowledged by criminologists that juvenile court trials, with attendant stigmatization of the convicted offenders, are sometimes more detrimental than beneficial to the offender in preventing subsequent crimes, their deterrent effects upon potential juvenile offenders have never been disproved. On the other hand, the effects of official police warnings upon their recipients have never been analyzed, despite the dramatic increase in this type of juvenile justice diversion in the last decade, compared to the numbers of young offenders tried in juvenile court. Official police warnings behind closed doors may curtail rather than enhance safeguards for the rights of minors. The police have been accused of favoring this diversion when they do not have sufficient evidence to secure a conviction. By the same token, it has been alleged that the police prefer to give a juvenile delinquent an official warning and then forget it, rather than refer him to youth protection services that require time-consuming follow-ups. The dejudicialization processes for minors in England (as well as in other countries, such as the United States of America) need to be justified by statistical data to increase the use of police warnings to juvenile delinquents as an alternative to juvenile court or youth protection service referral. Forty-one references and three graphs are appended. --in French.