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"If I'm honest it's a mystery to me," Don Warrington – who plays the Commissioner – tells RadioTimes.com. After some consideration, he adds: "It is different to any other show in that it's a crime drama but it's also so much more than that. It takes a light look, if you can say such a thing, at crime.

"There's a little bit of blood but there's not much blood. And I think it's the shoehorning of humour into such a heavy situation."

The Commissioner is a native on the fictional island of Saint Marie, but the Detective Inspector (O'Hanlon) only joined the series at the end of series six, inheriting a much-loved show that had already found its groove. Creator Robert Thorogood's formula, established in episode one, has barely wavered even 56 episodes later.

"What probably lends itself to international sales and appreciation worldwide is the formulaic nature of it," newcomer O'Hanlon says.

"It's quite simple. You know exactly what you're getting every week. You're going to get an ingenious puzzle, which is going to be at the heart of it all. You're going to get a little bit of comedy banter between the two uniformed police [Dwayne and JP].

"So people know what to expect. And I think people in a childlike way enjoy that. I think that the show is designed quite cleverly in that sense. You're going to get a little bit of an insight into the domestic situations of the various characters, so it's a balancing act between comedy, very light drama, it's very accessible and it looks gorgeous."

It's a tried-and-tested formula that fans love. We start off with a dramatic, slightly outlandish, often "impossible" murder, which is immediately followed by the upbeat theme song: Jamaican sixties hit You're Wondering Now. The cops arrive on the scene, inspect the body, identify 3-5 suspects, look for clues and follow false leads. Forty minutes later, someone (usually the DI) has a brainwave, solves the puzzle and gathers his suspects together to tell them who is guilty and how they did it. The murderer (usually) confesses and is taken away in cuffs. Then the police go for a beer. The end!

"This is not in any way a criticism of the show, but we do spell it out," O'Hanlon says. That's part of why it translates so well to different languages and cultures across the world: there's no room for misunderstanding.

"So if you had a little nap at any stage during the show" ["which you won't do," Warrington interjects] "– which you could never do because it's so dynamic and exciting – but if you did and you woke up again, I'd be there recapping in the police station, telling you exactly what you missed. So I do think it's cleverly designed."

Death in Paradise is filmed in Guadeloupe, but is set on the fictional island of Saint Marie. O'Hanlon thinks this also adds to the show's international appeal.

"Another potential reason is that it's clearly a fantasy world," he says. "It's not really rooted in any specific island. Like it's kind of a French island or a British island, what is it? So it's almost like an island designed by committee. By world committee. By the illuminati, actually, have designed this show. Because it's so clearly a fantasy, it's not rooted in any sort of gritty urban milieu.

"It's kind of like it subscribes to a fantasy that everybody shares to some extent. That desert island fantasy. Most people at some time or other in their lives – no matter where they grew up – will have had that fantasy."

Death in Paradise will return for season eight in 2019. Ardal O'Hanlon and Don Warrington were speaking to RadioTimes.com at the BBC Worldwide Showcase in Liverpool