Britain's top police officer said the relaxation of cannabis laws should not be reversed as dealing with small amounts of the drug wasted police time.
Sir Ian said the Met will pursue cannabis importers
Sir Ian Blair said if the law was changed he would like to see Fixed Penalty Notices for people possessing small amounts of cannabis.
His comments came as an advisory body which recommended the drug's downgrade to class C reassessed its decision.
Charles Clarke asked for a review after a suggested link with mental illness.
The home secretary also asked the Advisory Council on the Misuse of Drugs (ACMD) to consider the issue of high-strength cannabis, known as "skunk".
There is no point a police officer spending hours dealing with something the courts and the CPS don't do anything about
He said the Dutch government was looking into whether cannabis above a certain strength should be given a higher classification.
The reclassification of cannabis in January 2004 made most cases of cannabis possession a non-arrestable offence.
The Metropolitan police commissioner said: "In London, in my view we should stay where we are."
Sir Ian said the courts and the Crown Prosecution Service had "consistently failed to do anything about" the possession of small amounts cannabis.
"There is no point a police officer spending hours dealing with something the courts and the CPS don't do anything about," he said.
But the police chief stressed the Met was continuing major operations against cannabis importers.
He said if there was a law change the force would push "very hard" for Fixed Penalty Notices, but he did not say how much fines would be.
Mr Clarke wrote to the ACMD in March, highlighting concerns over several studies that strongly linked cannabis use to the development of psychosis.
Cannabis was downgraded to class C in January last year
He also wrote that since the downgrading of cannabis there had been no proven increase in use of the drug.
A study by New Zealand scientists, published in March, suggested smoking cannabis virtually doubled the risk of developing mental illnesses such as schizophrenia.
Putting cannabis in class C placed it alongside steroids and some prescription anti-depressants.
Shortly before the general election, the prime minister said the decision to downgrade the drug was being looked at again amid new evidence cannabis "isn't quite as harmless as people make out".
BBC home affairs correspondent Daniel Sandford said there are concerns over "skunk" which has seen its active ingredient THC doubled from 6% in 1995 to 12% in 2002.
He said the process of examining the drug's reclassification will continue until December.
"The experts meeting today are by no means guaranteed to recommend that any form of the drug should be moved back to Class B," he said.
Marjorie Wallace, Chief Executive of the mental health charity Sane, said she hoped the advisory body would consider "mounting research linking cannabis to the increase in drug-induced psychosis".
She said if the government did not consider the drug's reclassification, it should invest in campaigns warning young people of the drug's dangers.
"While we do not yet know in what way cannabis is linked to schizophrenia, we should not be placing young minds at risk," she said.