Karl Ove Knausgaard interview: The Norwegian literary sensation on his My Struggle series, and the next instalment - about Hitler's childhood

When I interviewed the Norwegian literary sensation Karl Ove Knausgaard in 2013, the second in his six-volume My Struggle series of autobiographical novels (A Man in Love), was receiving rapturous reviews and attracting a devoted readership. The novel described in hypnotic detail Knausgaard's life as a middle-aged husband, father and writer. Subsequent volumes have focused on his childhood and youth. "After Book Two, I needed to go into my past so the reader would have more knowledge of the narrator," says Knausgaard when we meet to discuss Book Five, Some Rain Must Fall (Harvill Secker, £17.99) – "The books were getting attention [by then] so I started being kinder about the people who appear as characters."

As we talk, I refer to "the narrator" of My Struggle, in part because the stylish man sitting opposite me looks far removed from the insecure twentysomething we read about in his new novel. "He's still inside me," says Knausgaard when I ask if, at 47, he feels like the same person as his narrator. "I have more experience but the same core. It's the closest I've managed to get to myself in writing. The challenge was to write about my past as if I didn't know what was going to happen and without irony. It involves getting into character through language."

Some critics were disappointed by Book Three but it contains the best writing on childhood I've read this side of James Joyce. Book Four was baggy and meandering but Some Rain Must Fall, which chronicles his student years in Bergen through to his first marriage, is Knausgaard at his best. "Each book can be read as a standalone novel," he says before explaining that he wrote the 660-page fifth volume in eight weeks in 2010: "Being in the flow feels close to joy but writing this book was painful because I felt embarrassed and ashamed of what's in it."

The narrator spends his caffeine-fuelled days writing stories and reading, among others, Paul Celan, Dante, Thomas Bernhard. As Knausgaard pours our coffee, I ask how many cups he drinks per day: "Many. But I don't keep count." My Struggle can be hilarious but, in the new novel, the narrator's boozing gets out of control. He upsets his girlfriends, alienates friends and vandalises his neighbourhood. Yngve, his older brother, insists: "You've got to stop drinking." Has Knausgaard followed Yngve's advice? "More or less. My problem is that after two beers I get the hunger for more and get terribly drunk."

What does Knausgaard think of the way he treated women in his twenties, cheating on his girlfriends for example? "I don't know," he says. "There's innocence about the male immaturity I'm describing but its results can be hurtful." His classmates at the Bergen Writing Academy mocked his stories and later he envied two friends who published well-received debuts, so did he ever stop believing he would succeed as a writer? "Yes," he says, "in my mid-twenties everything I wrote felt untrue." His first novel, Out of the World, however, appeared in 1998: "I don't know where the change in my writing came about. It was probably part of growing up." Does he still suffer from self-doubt? "Yes, I'm writing four books now, they're named after each season, but they lack the feeling of authenticity."

Knausgaard's terrifying father, whose death dominates Book One, is a diminished figure in volume Five. "This man who had once had the strength and magnetism of a king… There was nothing left of him," writes Knausgaard and today he says: "I used to be unable to forgive my father for making me afraid of him but now I think there's nothing to forgive." I wonder if Knausgaard's anguish about his father is connected to a broader desire for other men's approval. In an essay about Knausgaard and gendered literature, Siri Hustvedt, an early champion of My Struggle, writes: "Male status, pride, and dignity revolve around what other men think. Women don't count." For all he's written about his father's withholding of affection, could Knausgaard's loving mother be his books' overlooked hero? "'Hero' is a strong word," he says, "but I like that idea. My father was taking from me whereas my mother gives me something. It's harder to write about what people give you."

How did his first wife, Tonje, react when My Struggle appeared after they divorced? "Tonje was upset by reading about things I did while we were married that she didn't know about," says Knausgaard. "She made a radio programme about being part of this project. That was a good way of taking back control. There was conflict when the book came out in Norway but, last year, I met Tonje in Bergen and it was good to talk with her." In Some Rain Must Fall, their marriage falls apart after the narrator betrays Tonje by sleeping with a woman whose boyfriend accuses him of rape. The allegation is unfounded but was, Knausgaard says, "very, very unpleasant to write about."

We go out on the terrace so Knausgaard can smoke and, as rain speckles his Chesterfield, I mention his narrator's taste in music. In one memorable scene, he vomits at a party at Björk's apartment in Reykjavik, but his passion is for Manchester bands of the early-1990s. "Growing up, listening to British music was my way out into the world," says Knausgaard. Recently, he and Yngve reformed their old band, Lemen: "The only advantage of my books doing well is that people come to our gigs," says Knausgaard who plays drums but, at 6ft 5 ins, looks like a bassist.

Don Bartlett's English translations of My Struggle have appeared annually since 2012. Next year's final volume will bring the series full circle by charting the fallout from the publication of Book One and contain 400 pages about Adolf Hitler's childhood (and inclusion of Anders Breivik). It's a rare novelist who writes about student bars and the Happy Mondays at the same time as yearning for spiritual salvation. "What I experience in art is a substitute for religious ecstasy," says Knausgaard and My Struggle offers its readers similar rewards. He's revolutionised autobiographical fiction and reached more readers than he ever anticipated: "People relate My Struggle to their own lives," he says. "When they read it memories come back to them. It seems like we have all had the same life."