The Mayor of London, who on Thursday welcomed the government’s “U-turn” in making face coverings compulsory in shops, revealed that the prime minister has not been in touch for much of the coronavirus crisis.
Khan said he had been lobbying on the use of face masks since early April, adding: "The last time I spoke to him [Johnson] was the last time there was a Cobra meeting, which was in early May.
"I find it astonishing the prime minister of a country during a pandemic isn't holding Cobra.
"I find it equally astonishing that the prime minister isn't engaging with the mayor of the capital city.
"It's for him to explain why he's not doing so, I'm keen to make sure that we make London as safe as we can during this pandemic and our teams work with the government, even though it's not the prime minister."
Face coverings will be mandatory in shops and supermarkets on Friday, something that Khan said was “long overdue”.
He added to the PA news agency: "The evidence is quite clear, wearing a face coverage stops you passing the virus on particularly if you're pre-symptomatic or asymptomatic.
"I think it's really important, everyone across the country follows this advice, and in fact it's the law now, and us doing so will keep the virus under control.”
Under the new face covering rules, people will need to have their nose and mouth covered or face a fine of up to £100.
People with certain disabilities will be exempt.
It comes after rules requiring people to wear face coverings on public transport became mandatory last month.
Initially many experts and authorities, including the World Health Organization, suggested face coverings were not effective in preventing the spread of COVID-19 but are now recommending wearing them in indoor spaces.