Wearing masks to avoid spreading COVID-19 might have some advantages, the transport secretary has said.

Grant Shapps explained the policy was under review by the government's chief science advisers and cautioned the face coverings may even be "disadvantageous" if worn wrongly.

He has been urged by the mayor of London to make wearing masks on public transport in the capital compulsory to stop the outbreak of coronavirus.

Image: Mr Khan said the move would protect staff as well as passengers

Sadiq Khan told Sky News that "although it may not stop you catching the virus, what it does do is stop you passing on the virus if you're pre-symptomatic or asymptomatic".

"Where this is really helpful is in stopping the virus spreading in a place where you can't keep your social distance."


He said the Centre for Disease Control and Prevention in the US, chief public health officer in Canada and countries like Germany, Austria, Czech Republic, Mumbai, China and South Korea are all advising people to wear masks.

"What I'm not advocating for is for precious personal protective equipment to be diverted away from the NHS or care services," he cautioned.

London has been the worst hit region for coronavirus-related deaths, with all travelers to be told to board buses through the middle doors to protect drivers' safety after at least nine of them died.

Public Health England has emphasised the importance of masks for doctors and nurses treating patients with the coronavirus, but it has not suggested widespread public usage.

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However, the government's chief scientific adviser Sir Patrick Vallance said on Monday that the UK's position on masks was under review and would change if the scientific evidence warranted it.

Mr Shapps also told Sky News' Kay Burley@Breakfast: "It looks like the advantages might be marginal - there can even be times when it's disadvantageous if they're not used properly.

"We must be guided by the science in defeating this virus at every stage."

The WHO has said people should only wear masks if they display symptoms of COVID-19 or are taking care of someone who does.

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But it has also said that a mask on its own is not enough to protect people from the virus, emphasising the importance of other preventative measures like hand washing as well.

While there is no conclusive evidence to say that masks can stop people from contracting COVID-19, it is accepted that they can block transmission to others.

Image: Public Health England has not suggested widespread public usage of face masks

In April, a study in Nature Medicine suggested surgical masks could help prevent infected people from making others sick with seasonal viruses, including coronaviruses.

Jeremy Howard, a University of San Francisco research scientist and founder of the #Masks4All campaign, led a review panel with 18 other experts from around the globe and discovered "substantial evidence in favour of widespread mask use to reduce community transmission".

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Health Secretary Matt Hancock also revealed on Friday the government initially considered only locking down London, but ministers decided it was better the measures be rolled out "across the country as a whole".

"And that's for two reasons," he told a Commons committee.

"The first is that if you put a lockdown in one part of the country, then there's still travel from there to the rest of the country, so it isn't as easy as that.

"And the second reason is that actually one of the really strong things that's come through this crisis is that the country is acting in lockstep."