Downing Street has called on the public to wear their face masks properly after people have been spotted on public transport wearing them like chin straps.
The Prime Minister’s official spokesman said people should ensure their face masks cover both the nose and the mouth.
People have complained on social media about commuters wearing face masks only over their mouths or underneath their chins.
One Twitter user posted a photo of a man with a mask just over his mouth, adding: “Can someone educate people on the district line how to wear face masks. This is clearly the incorrect way."
The PM’s spokesman said: "Covid-19 is a respiratory disease. If someone has the virus, droplets can leave the nose and month and infect others when someone breathes, speaks, sneezes, laughs or coughs.
"Therefore, a face covering should cover both the nose and mouth to reduce the spread of coronavirus droplets, helping to protect others."
It is mandatory to wear face coverings on public transport. People are also advised to wear face coverings in enclosed spaces where they cannot maintain a physical distance from people they would not normally meet.
Asked about scientific reports calling for wider use of masks, the PM’s spokesman said: "It is something which we always keep under review.
"We have been very clear about the benefits of people wearing face coverings.
"Face coverings can help us protect others and reduce the spread of the virus if people are infected but not showing symptoms."
It comes as a leading UK scientist said no-one should leave the house without a face covering.
Professor Sir Venki Ramakrishnan, president of the Royal Society, said the UK "way behind" many other countries in using coverings to protect against the spread of coronavirus.
He pointed to mounting evidence suggesting masks protect both the wearer and those around them.
