The mercury has plummeted in the capital, with last night reportedly one of the coldest this winter as the temperature fell below freezing.
Sparing a thought for those without a roof over their heads, London Mayor Sadiq Khan responded by opening emergency cold-weather shelters.
Khan urged people on social media to report sightings of rough sleepers to the homelessness charity Streetlink, which connects them to local services and support.
We've opened emergency cold-weather shelters to help those sleeping rough in tonight’s freezing weather. https://t.co/H9csrWqu0e
— Mayor of London (@MayorofLondon) January 4, 2017
If you see someone sleeping rough in this cold weather, please help by reporting it: https://t.co/H9csrWqu0e
— Mayor of London (@MayorofLondon) January 4, 2017
"We’ve opened emergency cold-weather shelters to help those sleeping rough in tonight’s freezing weather," he tweeted yesterday. "If you see someone sleeping rough in this cold weather, please help by reporting it."
The mayor's message remains relevant as tonight looks set to be as cold as last night.
There are signs Khan's posts are already making a difference, with Londoners taking to social media to say they'd contacted the charity during the cold snap.
@shirley_wheeler @MayorofLondon me too :)
— MissP (@LpPeer) January 5, 2017
Khan also encouraged the public to "stay warm” and "look out" for each other, posting a link to NHS advice for keeping cosy and watching out for vulnerable neighbours and relatives.
The advice includes having regular hot drinks, eating regularly and wearing several light layers of warm clothes, rather than one chunky layer.
The mayor's call came as the Met Office warned the public about dangerous patches of ice in parts of the U.K.
You can report sightings of rough sleepers around the country to Streetlink here.