Sadiq Khan would be wasting his time if he sets up a review to look at decriminalising cannabis if he is re-elected as London mayor, Downing Street has said.

Boris Johnson’s press secretary Allegra Stratton said the prime minister has “absolutely no intention of legalising cannabis”, insisting “illicit drugs destroy lives”.

Khan has promised to set up an independent commission to examine the health, economic and criminal justice benefits of decriminalising the class B drug.

The review would likely look at evidence from Portugal, several US states, Canada and Uruguay, where cannabis is effectively legal for recreational use.

The London mayor has said it is “time for fresh ideas to reduce the harms [that] drugs and drug-related crimes cause to individuals, families and communities”.

Khan said: “The illegal drugs trade causes huge damage to our society – driving serious and violent crime, damaging people’s health and criminalising too many young people.

“That’s why, if I’m re-elected, I will establish a new London drugs commission comprised of independent experts to examine the latest evidence from around the world.

“The commission will make recommendations focusing on the most effective laws to tackle crime, protect Londoners’ health and reduce the huge damage that illegal drugs, including cannabis, cause to our communities and society.”

But Stratton told reporters: “Policy on controlled drugs is a matter for the UK government and there are no plans to devolve this responsibility.

“The prime minister has spoken about this on many occasions – illicit drugs destroy lives and we, he, has absolutely no intention of legalising cannabis, which is a harmful substance.”

Asked if Khan would be wasting his time with a review, she replied: “That is correct.

“Sadiq Khan, the mayor of London, will know that the policy of controlled drugs is a matter for the UK government.

“It’s not a matter for his office.”

Stratton meanwhile defended Johnson using Downing Street coronavirus briefings to make political attacks on Khan over Transport for London’s finances, which the mayor has described as “lying”.

Politico’s London Playbook on Tuesday reported that the BBC has held talks on how to handle the Covid press conferences if the PM continues to use them to launch political attacks on prime time TV in the legally sensitive period leading up to May’s local elections.

Stratton said: “The prime minister was asked a direct question by a CityAM journalist about what was being done for London during the pandemic and the prime minister was simply answering a direct question.” 

The press secretary also defended Johnson’s visit to a church which has been widely criticised for its attitudes towards homosexuality.

Labour leader Keir Starmer has apologised for visiting the Jesus House for All The Nations church in Brent, north London.

Asked if the PM would do the same, Stratton said: “We remember the visit to Jesus House well, because that day it was the site of a pop-up centre for vaccines.

“One of the main jobs inside government over the last few weeks and months has been driving up vaccine take-up in communities that are hesitant about taking it, most notably the Black community.

“That was the purpose of his visit that day, it was a profitable visit where he was able to meet Black community leaders and work to increase vaccine take-up and deal with vaccine hesitancy.

“So it was an incredibly important visit – making sure every aspect of the population feels confident in and takes the vaccine is a top priority for this government and that’s why the prime minister made that visit that day.

“Hopefully people don’t need reminding, but in case they do, this is a government that is fully committed to advancing LGBT rights and championing equality.”