She was, she said, “away with the fairies”. She was drinking and smoking from the moment she woke up. “A pint of Strongbow” and “20 Mayfair” were often the only words she spoke. “I was doing it,” she explained, “because it was something to do. I used pubs like day centres, because nobody knows who you are.”

When Sarah Wheeler told me that she had been away with the fairies, she didn’t mean that she was feeling a bit fed up. What she meant was that she was battling the psychosis that she has had to live with since she was eight years old. It has driven her, at times, to sleep in empty houses because she couldn’t face the chaos of her “rabbit hutch” flat. She couldn’t manage her money. She couldn’t manage housework, or meals. She spent two years sleeping on people’s sofas and living in bed and breakfasts.

Sarah has been diagnosed with borderline personality disorder, bipolar disorder and depression. She has tried to kill herself 13 times. And 13 times, thank God, she has failed to kill herself. No wonder, when she had the idea for a “creative endeavour”, she decided to call it Mental Fight Club. The battles she has fought make Brad Pitt’s fisticuffs look like the Sugar Plum Fairy’s pirouette.

You wouldn’t guess any of this when you meet her, at the weekly pop-up cafe she has started in a church crypt. What you notice, when you walk in on a cold winter’s day, is the warmth. There’s singing, and art, and writing, and bean bags, and massage, and fairy lights, and cakes. There are even little rose bushes in pots on a carpet laid out like a lawn. They made me think of Louis MacNeice’s poem about snow and roses. “World is crazier,” says MacNeice in Snow, “and more of it than we think.”

There is certainly something “crazy” about the Dragon Cafe, which Wheeler founded in the crypt of the church of St George the Martyr, in the London borough of Southwark, and which marks its 100th Monday opening next week. It’s “crazy” not because it’s aimed mostly at people who have struggled with mental illness, but because it seems like an almost crazily visionary project in an often cruel world – many of the people who come to the cafe spend most of their time on their own, and many are living in fear of having their benefits slashed.

“The whole point,” Wheeler told me when I went there this week, “is to be a complete antithesis to your average mental health service.” People like it, she said, because there’s “no pressure to do anything at all”. They can sing, if they want to. They can write. They can paint. But they can also just collapse on a bean bag and snore.

The cafe is run by volunteers. Many of those have known what it’s like to be mentally ill. “We keep it simple,” said Wheeler. “You don’t have to do anything outside your four-hour shift.”

And what they do in those shifts is make “an open-hearted place”. In other words, they make a place that can seem like a kind of heaven when you have been in a kind of hell.

I was never sure what David Cameron meant when he used to talk about the “big society”, but I think he would find it here. He would find people who have been through terrible things, and who know what people who have also been through those things need. He would find volunteers who love their role, and are properly trained, and turn up. And he would find people who are often made to feel like the scrapings at the bottom of society’s barrel getting a tiny taste of what it feels like to be treated with respect.

The Dragon Cafe has some funding. But to survive, it needs much more. I really hope the place gets it. I also hope that dragon cafes, or phoenix cafes, or whatever you want to call them, will spring up throughout the land. Mental healthcare, said the Royal College of Psychiatrists this week, “is at breaking point”; and yet another trust faces being placed in special measures. Even if you are given the right bed, in the right place, that place can still feel pretty damn cold.

My sister had her first breakdown when she was 14 years old. Going into hospital only made her worse. One of the things that kept her going was a cafe that she went to three times a week. It had been started by someone whose brother had schizophrenia. It was funded by grants and run by volunteers. It was a place where people used to fighting daily battles with their mind could paint or cook or sew. It was a place where they could get some respite from that fight – a place where they knew they were not alone.

When my sister died, her friends at the cafe clubbed together, and in the tiny garden they planted a rose. Let’s plant more roses like this.