Sadiq Khan today announced he has set up a new body to look at whether cannabis should be decriminalised in the UK.
The London mayor has established the capital’s first London Drugs Commission to “examine the effectiveness of our drugs laws on cannabis”.
While he does not have any power to decriminalise drugs, and has not pledged to do so, Mr Khan said public figures must “reduce the huge damage that illegal drugs cause to our communities.”
And Labour peer Lord Falconer, the new head of the Commission, said: “A national debate is long overdue.”
But Home Secretary Priti Patel hit out, tweeting: "Sadiq Khan's time would be better spent focusing on knife and drug crime in London.
Mr Khan praised the "high standards" of legalised cannabis farms in the US during a tour of the country
“The Mayor has no powers to legalise drugs. They ruin communities, tear apart families and destroy lives."
Labour also distanced itself from the plans, with a spokesman saying the party "does not support changing the law on drugs".
He added: "Drugs policy is not devolved to mayors and under Labour would continue to be set by national government."
Mr Khan praised the "high standards" of legalised cannabis farms in the US during a tour of the country.
His office said cannabis arrests in California dropped by 56% after it became legal to use, possess and grow it in 2016.
Allies also said a YouGov poll had found 52% of Brits backed decriminalising the drug compared to only 32% who were against.
The Commission will use research from University College London and particularly focus on the class B drug cannabis but will not consider class A drugs.
Mayor of London Sadiq Khan at Traditional, a licensed cannabis cultivation business in Los Angeles
Mr Khan told the PA news agency an "honest, open" conversation was needed about UK cannabis laws and he hopes the panel will look at "what happens elsewhere in the world where the laws have been changed".
During the four-day tour, billed as a "fact-finding mission" to investigate an international evidence-based approach to reducing drug-related harm in London, Mr Khan visited a Los Angeles cannabis dispensary and farm as well as a shop that sold products infused with the drug.
Describing the farm as "heavily regulated" with "really high standards", he said: "It's important to see for ourselves what the parallel world of legalised cannabis looks like as a compare and contrast."
Mr Khan said an "honest, open" conversation was needed about UK cannabis laws, adding that visiting the facility had been "fascinating".
"We need to have an honest, open conversation about the evidence in relation to the history of cannabis and our laws in the UK and our experience of the health consequences in relation to crime and the community," he said.
"The best way to do that will be with the drugs commission we've now set up.
"You can hear from the experts, that's one thing, but seeing it for yourself … hearing from those who cultivate and grow this plant has been fascinating."
On his opinion of the facility, he continued: "(It) is quite clearly heavily regulated, there are really high standards, no corners are being cut, they're readily inspected by the city, by the experts.
"It's important to see for ourselves what the parallel world of legalised cannabis looks like as a compare and contrast.
"What I hope the London Drugs Commission will do is look [at] what happens elsewhere in the world where the laws have been changed."