Big companies should carry out random drug tests on their staff, Shaun Bailey has said.
The Conservative London mayor candidate said the aim of mandatory drugs tests on staff would not be to get people fired, but to change the culture around drug use.
People who buy drugs are "funding the criminals who...unleash mayhem" on London's streets, he argued.
London is by far the biggest consumer of cocaine in Europe with a market worth £1 billion per year, a study by King's College London claimed last year.
In an open letter addressed to London’s business leaders, he wrote: "This is a huge problem. Drug use is not only a crime in itself; drug use is a direct cause of crime, from county lines gangs to stabbings on our streets.
"When people buy drugs, they are funding the criminals who traffic vulnerable kids and unleash mayhem on our streets.
"So as mayor, I’ll call for every business in London with over 250 employees to sign up to a drug testing charter."
Mr Bailey, 49, who grew up in a council house in Ladbroke Grove, west London, was a youth worker with gang members for 20 years.
"The purpose of this charter is not to get employees fired or shamed. Individual results will be anonymous,” he said.
"The purpose is to change our culture. City Hall will publish an annual league table showing which companies have the highest and lowest rates of drug use.
"Because…the way to start tackling a problem is to shine a light on it."
Additional reporting by the Press Association
