On a cold and windy November night in central London, people are huddling into their thick coats and cosy fleeces. But at Spitalfields market, trainee solicitors Emily Blanshard and Caroline Hartley are preparing to spend the night sleeping outside.
"This isn't the same as sleeping rough, but we wanted to give support to people who are, and raise money for a good cause," says Hartley.
More than 400 people are joining them in spreading their sleeping bags on the cold concrete, including celebrities such as radio DJ Sara Cox and the Arsenal FC CEO, Ivan Gazidis, while Dan Gillespie from the Feeling is on hand to give an exclusive performance. This is the Centrepoint annual sleep out, which the charity organises every year with the aim of raising money to combat youth homelessness.
Centrepoint works to improve the lives of homeless people aged 16-25. It provides a range of accommodation, including night shelters, hostels and flats, plus a range of other services they might need.
People who are supported by Centrepoint have experienced difficult backgrounds, including abuse and family breakdown. Many of them will have slept on the streets, with all the danger, discomfort and impact on health that implies.
Yet they have so much to offer. The CEO of Centrepoint, Seyi Obakin, says: "The vast majority of the young people we work with want to do well, they grab the opportunity with both hands. All we need to do is give them the platform. Then they can set about unlocking the potential that is in them."
Tres B is one of those who has grabbed that opportunity. He came to the UK as a refugee from the Congo six years ago, when he was 16, in circumstances he finds difficult to talk about. He lived on the streets for a year but was then given accommodation by Centrepoint and was able to pursue his interest in music.
With the ambition of becoming a "superstar", Tres B has already performed his mix of African music, hip-hop and R&B at the Big Chill and iTunes festivals, and is at the sleep out as one of the night's entertainers.
"Being homeless is very hard," he says. "But now I am focused on my goals."
Of course, most people at the sleep out have not been homeless. Liam Butler is here with colleagues from the Conran Shop, which has chosen Centrepoint as the charity for which it will raise money this year. "We are promoting very expensive furniture and we felt the most sensible choice for our charity was something that puts a roof over people's heads."
Yvonne Nelson is a careers adviser in her working life, and is staffing a stall offering insulated mugs. "I'm giving up my time to support those people who are giving up their time for this good cause," she said. Nelson is also making her involvement more long term. "I'm going to become a volunteer mentor. Hopefully I can make a difference."
Butler and his colleagues are laughing and joking as they prepare to hunker down for the night. "We're lucky on a night like this to be covered," he says. "You aren't actually on the streets. It just gives you a tiny taste of what it's like."
Centrepoint's Christmas campaigns
At Christmas, the difference between those of us who have warmth and security and those who don't becomes even more stark. So why not reach out to a homeless young person through Centrepoint?
Homeless young people have often had a difficult start to life, with abuse, poverty, family breakdown and substance abuse pushing them on to the streets. However, you can help them into a warm, safe room, where they will also be helped with other challenges they may be facing, such as lack of education or ill-health.
By sponsoring a room, which costs just £12 a month, you are offering the gift of warmth and the chance of a new beginning. Why not go to centrepointroom.org.uk/warmth and find out more?
