"This book is not about the interesting, fascinating story. That would be too easy. It is about people who are affected by a story but who feel insignificant. It is about being in a place that is not anywhere in particular, about not being the person who is the main event."
In The Approaches is marginal in other ways. Amazingly for a 500-page tour de force of dramatic monologues, it is, Barker says, a minor book that is a subsidiary of a larger work-in-progress. "They always interrupt a longer third-person narrative which I am getting stuck on. Often it will be related to ideas in the bigger book that I can investigate more closely. I feel a spirit of mischief."
Life on the periphery - toppling sometimes toward the centre of things but just as often spinning off into the universe - is very Barker. You only need to glimpse at her Amazon ratings to see how her unbridled, experimental novels like The Yips and her masterpiece, Darkmans, separate the fanatics from the detractors. "I think this book might divide people, but I'm okay with that. As a writer, death is consensus. When you see the things that everybody likes ... " Barker sighs, before laughing. "I am happy to confound people."
We talk in a large, deserted Thameside pub close to her Wapping flat. I have never interviewed anyone quite like Barker. She is intense and funny, but also acerbic and refreshingly unguarded. A discussion about representing spirituality in the modern age inspires an exasperated assault on Philip Pullman's fiction.
"To me, it's like he's the anti-Christ. Don't teach children not to believe in goodness before they believe in goodness," Barker pauses. "I have never read his work, so what do I know? But I just have a suspicion about it. I was a very spiritual child and the idea of that being taken away by fiction makes me very sad."
Barker doesn't really do small-talk. Our real-estate banter leads quickly into a disarmingly frank unpicking of Barker's "lively" dream life which is filled with floods, dilapidated houses, and a feeling of "inundation". Barker traces this mood of claustrophobic vulnerability to her formative years when her parents left England and settled in South Africa.
"I think it all comes from having emigrated from an island to a great continent. When I lived in Africa it was a very uncontrolled phase in my life. I looked back to an island as a psychological retreat. Perhaps fiction itself is a little island, a little safe place."
Literature as sanctuary is reflected by a composition process that is famously intense and immersive. "When I am finishing a really big book, it does take over my whole life. With Darkmans that process was two years. It is an all-encroaching world of language and of characters you invented to entertain yourself. It is quite self-indulgent. You think you are suffering terribly, but afterwards you think, I really enjoyed that phase and I just didn't want to see anyone."
Something of the visionary hermit lingers around Barker, whose devotion to her work removes her from the everyday, who craves communion with her imagination that is direct and unmediated. "Mystery is everything to me. I don't like to have everything analysed, torn apart and put back together again in terms of the construction of fiction.
Even if I am just the sum of my influences, I like to pretend that I live in a world which is me being creative."
This empathy with the ineffable has strange if explicable origins. A severe bout of bronchial pneumonia as a child damaged her pineal gland. "The cone in the centre of the brain which controls life and death, waking and sleeping. Descartes calls it the seat of the soul."
In the short term, the illness led to fits. In the long term, it left Barker with no sense of direction ("don't put me in a car") and a bizarre sleep disorder. "In the period between waking and sleeping, I sometimes suffer miniature deaths. I stop breathing and my body dies. Or the mind wakes up and the body is dead. The thing I get mainly is hallucinations." These include a giant spider, a ceiling of "compressed water" and geometric patterns.
One side-effect is that Barker, who has no clear-cut religious faith, nevertheless feels a powerful connection to mystical worlds. "The movement between spirituality and everyday life is more fluid for me. It is not as strange for me as it is for other people."
Another consequence is that she has no fear of death. "I have woken up and have been breathing out my final breath - the deepest exhalation when you feel the air going out of your entire body. I have had the utter sense that it was my last breath. The fear then is of wanting to be alive. But the actual exhalation is of great joy and relief."
Barker is craving the joy and relief of plunging back into her latest all-consuming magnum opus, a "very dark, late Victorian story that is based on a real story". She pauses.
"But who knows at this stage?" While her friends should prepare for months, if not years of going straight to voicemail, Barker herself is cheerfully resigned to her fate.
"It's just silliness. I like to take the work seriously, but by and large I don't take anything I do seriously. I am just a person who writes books."
In the Approaches (HarperCollins $34.99) is out now.
- Independent