There is a strangely cold passage in the first chapter of Dave Pelzer's latest book, where he meets a man called Joe at a book signing. Joe tells him sadly, "I just can't let go of all the crap in my life." Pelzer sizes up the man in a split second, decides "Ol' Joe might just be a little too comfortable with his sulky attitude," diagnoses a "wallower", and delivers a harsh public dressing down. Pelzer believes with "extreme conviction", he tells his readers, that in America "and other democracies like Her", there is simply no excuse for being unhappy. The king of the misery memoir may have built an empire out of hardship, but if there's one thing Pelzer can't stand it's a whinger.

Pelzer published his first book in 1995. A Child Called It was a horrific tale of sadistic abuse at the hands of his alcoholic mother, who kept him locked in the family basement, force-fed him dog faeces and ammonia, and stabbed and burned him. A sequel recounted his childhood in foster care after police and teachers rescued him at 12, quickly followed by a third volume charting his journey through the US air force to become a juvenile counsellor, bestselling author, motivational speaker and living legend of the daytime Oprah circuit. His books have been on the New York Times bestseller list for more than a decade, breaking every record since the list began.

British publishers doubted at first if his folksy rendering of almost pornographically obscene violence would appeal to British readers. But for "people who don't normally buy books", his UK publisher later marvelled, it proved irresistible. His first three books have sold more than 4m copies in the UK alone. Today Pelzer is credited with creating an entire non-fiction genre - misery literature - inspiring bestsellers from Constance Briscoe's Ugly to Augusten Burroughs' Running With Scissors.

After writing a further three self-help volumes which also mine his abusive past, he is now publishing his fourth. He says it takes him four hours to write a paragraph, and you certainly wouldn't take Pelzer for a writer; his tense stare and transatlantic casual wear make him look more like a salesman or banker. But his looks turn out to be the least of his anomalies. In person, Pelzer, 47, is by turn defensive, self-promoting, evasive, messianic - a torrent of intense sincerity and total contradiction.

He is out on the road more than 300 days a year, he says, putting in 14-18-hour shifts talking to injured troops, abused kids, social workers, pretty much anyone who asks: "Who are you going to say no to? It's a moral obligation." He still finds time to study the piano between 2am and 4am - yet "hasn't had time" to read a book by one of his own brothers about their childhood. He talks passionately about integrity - "I couldn't lie to get myself fame and fortune. At the end of the day I can hold my head high" - yet the veracity of his memoirs has been disputed by another of his brothers. He puts this down to his brother being "semi-retarded", stressing that "I'm very protective towards my brothers." But his brother suffers from Bell's palsy, a paralysis of the facial muscles, not a mental disability.

Pelzer insists book sales don't interest him - "that's yesterday's news" - yet mentions the New York Times bestseller list six times in a single hour. His new self-help book urges readers to leave the traumas of their past behind, but is the seventh volume to revisit his own. He is excessively polite and courteous, calling everyone ma'am and sir. But I notice he calls me "ma'am" most of all when my questions seem to be annoying him.

Pelzer believes people like his books because they put their own problems in perspective. "A Child Called It was a story about resilience, it was never about boo hoo hoo, it was about a kid that didn't quit. I never sat down and thought: I'll do it to commercialise it, or for morbid fascination. I did not know until I came to England, on a book tour in the late 90s, that there was this thing about a morbid fascination. That's when I was accused of it, of being a morbid writer. That had never happened in America."

How does he feel about the criticism that misery literature feeds a voyeuristic taste for cruelty? "I can't help what other people may think." But he must have an opinion, surely. "You know, that's not my job, ma'am. My job's to do a good job. That's my opinion."

He never intended to create a new genre, he says, and although he won't quite say so he clearly doesn't feel that his work belongs in it. "With A Child Called It, I was talking about something different, resilience instead of victimhood." He has read very few other misery memoirs, because "I'm always looking for a story of survival. Anyone can say I was divorced, my husband left me, my son died of cancer. But what did you learn from that experience, how can you be better and stronger for it? That's what I'm looking for."

His new book, Moving Forward, is essentially the American dream translated into another self-help manual. "I went from the worst case of child abuse, to receiving the Jefferson award." In other words, if Pelzer can make it, anyone can - and he gets impatient with people who show up at his talks and just don't seem to get it.

"A lot of people say, oh my God, I was abused 40 years ago. And I say yes, and I'm truly sorry about that, and I'll hug you and give you some advice, but you're going to have to decide what you're going to do. It's about a mindset. You can be a victim of cancer, or a survivor of cancer. It's a mindset."

For a man who by his own account has benefited enormously from therapy, and continues to, the idea that happiness is simply a decision seems to deny most psychotherapeutic principles. Pelzer even writes that his own past is just a "tiny fraction" of his life. If so, why does it constitute the main body of all his work?

"If I want to learn bodybuilding I'm not going to go to Pee-wee Herman, I'll go to Arnold Schwarzenegger. He's lived it. Ma'am, I never asked for this, I never designed it. As outgoing as I may seem I'm a very private person. I don't like the limelight, I'm an introvert. So what I'm trying to say is, maybe I'm supposed to be here. It's an awesome responsibility, and that's why I take it seriously."

His commitment to his work cost Pelzer his second marriage, and he lives apart from his son from his first. "But I believe it's like the Mel Gibson movie, Signs. Maybe things just click together for the right reasons. This is why I say for the record, this isn't me, this is way beyond me, no one could have planned it or dreamt it, no. The average stay on the New York Times list is three or four weeks, correct? We were on the New York Times list with one book for six years - and we did not spend one dime on PR."

He has, however, been accused of maintaining his position in the bestseller list by bulk buying his own books from stores, then signing and selling them at his talks. Given the sheer volume of his audiences, of whom a quarter on average buy a book, the strategy could plausibly work. He denies it emphatically - with such indignant innocence that it's hard to believe he'd ever knowingly tell an untruth. But he has also claimed A Child Called It was a Pulitzer prize nominee - when in fact it was merely a submission. For a fee of $50, I could submit my shopping list to the Pulitzer board.

"I was wrong," he says quickly, "I admit. I was told that it was nominated for the Pulitzer prize. That was my mistake. And since that mistake was brought up nine years ago, we haven't made that mistake since." But I logged on to the official Dave Pelzer website yesterday, I begin to say ...

"Doesn't say it there," he interrupts. But it does, I tell him.

"Well, I'll have it removed. Out of all the interviews in the world, you're the only one that's brought it up in nine years, ma'am." (When I checked yesterday, the claim was still on his website.)

By now Pelzer is looking pretty frustrated. He hasn't slept for three days since leaving home in Palm Springs, California, but I suspect the testiness owes more to exasperation that I'm not "getting" his magic formula of patriotic self belief and gutsy optimism. So I decide to stop asking any more questions, and let him hold forth.

"See?" he soon exclaims excitedly, "Now we can converse. Now we're discussing! I just love being a little kid, I'm an excited little kid. Oh my God, Indiana Jones is coming out! You catch me off duty, I'm the guy in the corner watching what's going on. I love weddings, I always bow to the bride! I love happiness! I'm a very happy guy. Every time I can pick up a cup of coffee or look at you, it's a blessing because I know what it's like to live in the dark.

"I can't convince people of that. If they want to judge me, they're going to judge me, but one thing I'm not going to do is chase my mother's approval. And that's a very big statement. A lot of people they're, like, well, Dave you're too naive, you're too nice, you're too good to be true. You know what? Fine. Fine. I don't have time for that. If they call me up and say Dave, you know what? We lost three states the size of Peru to Katrina, can you help us out? I say yes, I'll be there. You look at my vitae, my biog, I want what that guy's got, he's doing okay. And I've got a few demons, sure. But at the end of the day I know I gave it my best shot, and that's all you can do, and I'll do it the next day. And the next. And the next.

"If you have a gift, give it out. And I think now you're starting to understand that, aren't you? If you do, you do. And if you don't - well? It is what it is, ma'am".