The Home Secretary said Mr Khan’s time would “be better spent” focusing on tackling crime in the capital after he announced he was launching a commission to assess the effectiveness of UK drug laws.
Mr Khan praised the “high standards” of legalised cannabis farms in the US during a tour of the country, as he announced the formation of the new group to consider the decriminalisation of the drug in Britain.
In a rebuke on Twitter, Ms Patel said: “Sadiq Khan’s time would be better spent focusing on knife and drug crime in London. The Mayor has no powers to legalise drugs. They ruin communities, tear apart families and destroy lives.”
Labour 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.”
Former justice secretary Lord Charlie Falconer QC has been appointed as chairman of the first London Drugs Commission, which will use research from University College London and particularly focus on the class B drug cannabis but will not consider class A drugs.
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.”