Chantelle doesn't look biblical. Her big hair is held back with a red and white polka dot bow and her neon green bra shows at the shoulder. But like Mary in the Christmas story, this 21 year old is homeless, and turned up pregnant with an unmarried partner at an unlikely inn. It's just that her Bethlehem is south London, and her stable is a school canteen in a pop up shelter.

"It's somewhere to go isn't it?" she says, "My dad's a junkie, my mum's a bitch and I can't afford a deposit... council houses are for young girls, like, really young, fourteen... I'm not priority."

I met Chantelle at Crisis. Christmas is supposed to be a time of miracles, and every year this charity pulls one off. Run by some 8,000 volunteers, this organisation makes sure no one has to sleep rough or alone in difficult accommodation over Christmas week. They do this by taking over buildings closed for the holidays -- schools, hospitals, day centres -- and transforming them into shelters. They're still running as you read this.

I'm not religious, but if there is something to the Christmas story, this has to be it. When Joseph and Mary were travelling from inn to inn, they couldn't afford private rents and welfare didn't exist. Like the guests at Crisis, they were cast out, judged and failed by the market and the state. Eventually they were given a place to stay out of kindness, and a space for animals was transformed into a maternity ward.

Like Crisis, the religious story is about the importance of keeping a door open to strangers. It's about action beyond resources and targets; it's about the power of compassion, time and human relationships.

Of course it's difficult. The centre I was working in didn't get the keys to the building until the morning guests arrived. With minimal checks and training, volunteers walk in and put on housing surgeries, stand up comedy shows, arts and crafts workshops and dentist consultations in classrooms. Identifying themselves by coloured badges, volunteers, who may never have met before, work together out of little more than blind good will.

Together, they get through the tragedy of a sick man's collapse, the anger of someone being denied a bed, the laughter of a bad cracker joke and the quiet, intimate conversation as a cigarette lighter sparks in the cold.

And you learn. These people all come from my area of south London. They are my neighbours, but they tell me about a world I don't know. You learn that you shouldn't assume that everyone who is homeless is sleeping rough; people are fiercely proud of temporary or unstable accommodation. You learn to interact with dignity and respect for guests who have many more years experience than you. I sat down with an ESOL teacher with a degree in psychotherapy and an ex-serviceman who travelled the world for twenty-eight years. You learn how thin the line is between finding it difficult to pay the rent, crashing with a friend, and queuing for a hostel.

Nor is it all dark and sad. If you live day-to-day, you don't have the space to worry too far into the future. There's a preoccupation with getting enough food, finding somewhere else to sleep, bumming your next cigarette and topping up phone credit. The freedom of strangers and endless free cupcakes opens up a precious space in these shelters for laughter that frequently touches volunteers as much as guests, who are often struggling with big concerns of their own.

We should learn from Crisis. Unlike some of the work we do directly through the state, this programme is not subject to much bureaucracy. It makes use of buildings that would otherwise be closed. And it is built on human relationships rather than transactional roles, helping to transform the volunteer as well as the guest. We should make it easier to replicate these miracles, not just in the capital over Christmas, but wherever and whenever our modern day Mary might turn up.

To find out more about Crisis Christmas, visit the site here [2].

Rowenna Davis is a journalist and author of Tangled up in Blue: Blue Labour and the Struggle for Labour's Soul, [3] published by Ruskin Publishing at £8.99. She is also a Labour councillor.