South Bank University's Criminal Policy Research Unit conducted a detailed study of the policing of cannabis in England. The study found that:
"One in seven of all known offenders in England and Wales were arrested for the possession of cannabis.
"There has been a tenfold increase in the number of possession offences since the mid-1970s. There is no evidence that this increase has been an intended consequence of specific policy.
"Possession offences most often come to light as a by-product of other investigations.
"A minority of patrol officers ‘specialise’ in cannabis offences: 3 per cent of officers who had made any arrests for possession accounted for 20 per cent of all arrests.
"Arrests for possession very rarely lead to the discovery of serious crimes.
"Officers often turn a blind eye to possession offences, or give informal warnings.
"Of the 69,000 offenders who were cautioned or convicted in 1999, just over half (58 per cent) were cautioned.
"The financial costs of policing cannabis amount to at least £50 million a year (including sentencing costs), and absorb the equivalent of 500 full-time police officers.
"The researchers conclude that:
"- re-classification of cannabis to a Class C drug will yield some financial savings, allowing patrol officers to respond more effectively to other calls on their time;
"- the main benefits of reclassification would be non-financial, in removing a source of friction between the police and young people;
"- there would be a very small decline in detection of serious offences, but this should readily be offset by the savings in police time."

Source

"Findings: The Policing of Cannabis as a Class B Drug," (London, England: Joseph Rowntree Foundation, March 2002), p. 1.
http://www.jrf.org.uk/sites/f…