The mayor of London has said that masks should be made compulsory on public transport, citing evidence that suggests face coverings reduce the spread of coronavirus.

Sadiq Khan said this measure would be an “additional protection” on top of social distancing, regular hand washing and other government advice during lockdown.

"The evidence I've seen is if you wear a non-medical facial covering it doesn't necessarily limit your changes of catching the virus," he told Radio 4's Today programme on Friday morning.

"What it does do, if you yourself are pre-symptomatic or asymptomatic, it reduces the chances of you giving the virus to somebody else.

"And so wherever you can't keep your social distance you should be wearing a facial covering."

In a Twitter post on Thursday, Mr Khan wrote: “I've lobbied the Government for some time now to make the wearing of face coverings obligatory on public transport.

His comments came shortly after a prominent scientist took health minister Matt Hancock to task for implying that face masks might not be effective.

Mr Hancock had earlier said that if face masks “don’t help, then it doesn’t improve the national effort to tackle this virus”.

Jeremy Howard, a data scientist at the University of San Francisco who recently led a review panel on the effectiveness of masks, said they could be “one of our most important tools”.

He cited the example of Taiwan, a country which has distributed face masks and has only had five deaths from the virus.

He also mentioned the WHO assistant director-general David Heymann's comments that masks were as or more effective against viral transmission than social distancing.

Earlier this week, Mr Howard wrote on Twitter: "Most scientific evidence points in the same direction: keep your droplets to yourself – wear a mask.”

Chris Whitty, England’s chief medical officer, said on Thursday that the government was continuing to review its advice on face masks.

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He said that the government's Scientific Advisory Group for Emergencies (Sage) was assessing whether they could be beneficial in certain circumstances.

"The evidence is weak, but the evidence of a small effect is there under certain circumstances," he added.

The WHO’s current advice is that outside of the healthcare profession, people who are healthy should only wear face masks if they are caring for someone with Covid-19 symptoms.

Dr David Nabarro, the health agency’s special envoy for Covid-19, has said that masks will be common in the wake of the pandemic.

Countries like Germany have started to encourage the use of face masks, with Angela Merkel saying earlier this week they should be worn in shops and on public transport.