Face mask to remain compulsory in London public transport after July 19

"If you want to use public transport in London, the rules are you'll wear a face mask," Khan said during an interview with ITV's Good Morning Britain program.

On Monday, Prime Minister Boris Johnson confirmed that as part of final phase of the roadmap out of the lockdown, most of the remaining restrictions in England would be lifted from July 19, despite the latest scientific modeling showing that coronavirus cases could reach 100,000 per day and the daily death toll could climb to between 100 and 200.

The decision means that wearing face masks will no longer be compulsory in shops and public transport and there will be no limits on the number of visitors to care home residences.

There will be no limits either on the number of people allowed to gather indoors or outdoors, and the one-meter (three-feet) rule for social distancing as well as the capacity caps on large sports and cultural events will be lifted. Nightclubs and all remaining businesses will also be allowed to re-open.

According to Johnson, since rules will be replaced by guidance, it will be a matter of personal responsibility for people to wear face masks in crowded places.

The Labour mayor of London said, however, that he is not prepared to stand by and put Londoners and the city's recovery at risk by not continuing to enforce mask-wearing.

"By keeping face masks mandatory we will give Londoners and visitors the reassurance and confidence to make the most of what our city has to offer, while also protecting our heroic transport workers and those who may be vulnerable and rely on the network to get around our city," Khan said in a statement.

The mayor's decision was welcomed by the general secretary of the Transport Salaried Staffs' Association union, Manuel Cortes, who claimed on Twitter it was a "great call" to help limit the spread of the virus and urged other transport operators in England to do likewise.