Sir Bernard Hogan-Howe says that drug-testing would help cut the number of users - as the risk of losing your job would act as a deterrent.
"It seems to me we have got to plant in people’s minds something to affect the demand as well as supply. You can think of many occupations where if you were working with a colleague you would want to be sure in fact that they were drug free."
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Before the final declaration on Friday, the Conservative candidate looked set to lose the City Hall race to Labour's Sadiq Khan.
The Tooting MP has been the frontrunner in the counting process ahead of Tory challenger Zac Goldsmith.
It's not just London where elections have been taking place today. There were council elections taking place across the home counties.