Image copyright PA Media Image caption Terry Deary (right) and illustrator Martin Brown launched the Horrible Histories books in 1993

Author Terry Deary has a pretty good idea of why his Horrible Histories series is so popular.

"The problem with non-fiction books is they're written by experts who wouldn't know a child if it jumped up and bit them on the kneecap," he says.

"The reason Horrible Histories has been a success is I'm a fiction author. I published 50 fiction books before I turned to Horrible Histories."

It's true, Deary's imaginative style has now taught several generations of children history in a way that is playful and engaging - something that delights parents almost as much as it does their children.

The author has been described by The Radio Times as "a man whose scatological, cartoonish but utterly factual style has put a firework under British history books".

So you might assume that after writing more than 60 Horrible Histories books and seeing them adapted into West End shows, a Bafta-winning TV series, a major film and an art exhibition, Deary would firmly consider himself part of the literary elite.

He doesn't.

"In the publishing industry, I'm a fish out of water," he says. "I don't do literary festivals. And I don't mix with the literati."

Image copyright Mark Douet Image caption The stage adaptation of Horrible Histories returns to London's West End this month

"Who goes to literary festivals? They are attended by parents whose children enjoy books. My target is children who don't read books. The sort of kids I grew up with. Going to a literary festival isn't going to reach new readers."

Which raises the question of how to break that cycle and capture that audience. "Through television. Cinema. Going to heritage sites," replies Deary. "Book clubs where they go around schools and sell books, and the children go and look at them and are given tokens. Get books into the hands of children, and let them be the judges.

"Whereas literary festivals very often go for the names. 'Oh, Julia Donaldson is a star name - if we get her, it's a little feather in our book festivals cap.' They compete with each other. It's a game that I don't play."

Indeed, Deary rejects many things that would traditionally come with being part of that literary game. He doesn't want a knighthood. He won't appear on Desert Island Discs.

Deary's background, he says, is what marks him out as an anomaly in literature. He was born in a poverty-stricken area of Sunderland in 1946. His mother was a clothes shop manager, his father a butcher. Books were not part of the culture he grew up in, and as result there was a perception that northern boys didn't become writers.

"I only know one northern children's writer now," he says - singling out Skellig author David Almond.

"There are 100 southern middle-class women [writing books]. And it's business. Southern middle class girls read books. So the publishers publish books for them. Northern working class lads don't read books, so why bother publishing books for them?"

Image copyright Getty Images Image caption The cast of Horrible Histories: The Movie at its premiere last month

The new stage show, Horrible Histories: Barmy Britain - Part Four, opens at London's Apollo Theatre this week and runs until the end of the month - perfectly timed to catch the English school summer holidays.

This show is written and directed by Deary's regular collaborator Neal Foster. Deary himself is busy working on next year's show. Of all the platforms Horrible Histories has been adapted for, theatre is the one he feels most comfortable with.

"I don't want to sound pretentious, but as a professional actor, where I started, I took my theatre experience into books. So going back into theatre is the easiest and most direct way I can think of. They're planning to do an escape room. Horrible History themed. You heard of them? I can't script that because it's not in my cultural background, but theatre is.

"In the TV series, the director said, 'we can't do the Holocaust'. But I did in the books. And so the books can still do things that television can't because of sensitivities. I understand that, but I don't know the rules [of TV]. In theatre, I've done so many plays down the years I know what I can get away with."

The latest stage adaptation of the books covers a lot of ground - Samuel Pepys, Richard III, Mary Queen of Scots, Elizabeth I and The Romans all feature.

"And there are things you don't expect," says Deary. "Like the English army mutiny against Henry VIII. Why did [the army] do that? Because they didn't get beer. And that is a human story."

During Henry VIII's reign, 7,000 English soldiers were sent to Northern Spain to help Henry's father-in-law, King Ferdinand, conquer the kingdom of Navarre from the French. But when the soldiers found they couldn't get any beer in Spain, only wine or cider, they mutinied. It's these kinds of stories that delight Deary.

"You imagine that somebody going to war is thinking, 'I'm going to die for my king and country'? No, I'm doing it because it's a job. And if I don't get properly paid, I'm going home, which shifts your perspective of cultural expectations, which is great."

Image caption The CBBC adaptation of Horrible Histories has featured figures including Queen Elizabeth I

A great deal has changed in publishing since 1993 - the year Deary's first Horrible Histories book came out.

In 2011, he told BBC Breakfast the publishing industry was "going down like the Titanic" because it wasn't adapting quickly enough to changing consumer habits. Eight years on, he's embracing technology more strongly than ever.

"I haven't read a book for five years," he says, pulling out a Kindle from his jacket pocket. "I've got 350 books on there. I love it.

"I shouldn't say this, because I get pilloried, but people worship paper and ink, for some reason. 'Oh you mustn't throw a book away or burn a book.' I don't care how it gets across. I want to change the world, through any medium I can find.

"It's about what's in my head, and what's in my reader's head, and how I express it... It doesn't matter if it's a book, an e-book, a play, television, an exhibition."

Which perhaps explains why Horrible Histories has indeed been adapted for pretty much all the platforms he mentions. The CBBC TV series in particular has been hugely popular - albeit slightly less so with some traditionalists.

"It's wonderfully exciting to watch. It has such a great sense of the past. It's fun, harmless stuff," TV historian Dan Snow told The Guardian. "But it isn't a serious look at the past... We shouldn't try to dress it up as brilliant history."

Deary unsurprisingly cares little what historians think, but he does acknowledge: "Horrible Histories distort history. If you're rich, powerful and Royal, then you're bad. I'm not very fair.

"Rulers are either cruel, or stupid, or both. And I can't find any exception to that, so I just keep on saying that."

He reiterates: "My whole career is aimed at changing the world, and changing the way people, especially young people, look at it. And that's what I'll do. Through any medium I can find."