Kenneth Branagh is standing in the vast living room of Fowl Manor, the sprawling fantasy home of Artemis Fowl. Fowl, as you will likely know, is the protagonist of the internationally bestselling series of science fiction fantasy books by Irish writer Eoin Colfer, whose series of stories made his name as Ireland's answer to JK Rowling.

This house, a small-scale castle, was first built in Colfer's imagination, and in the world of the story, is located somewhere outside Dublin. But now, it has been built, brick-by-brick by Disney on the edge of a film studio in Surrey.

Branagh is in the middle of a day's shooting of the mega-budget film adaptation of the first book in the Artemis Fowl series, and he wears the brisk, yet affable air of a man juggling a million tasks and issues with practised equanimity.

It's a juggernaut of a project, produced by Disney and slated for release in late summer 2019. Fowl Manor is at the centre of a vast and ambitious set that has been purpose- built at Longcross Studios - a world so detailed and monumental that it could rival Potter.

The project is freighted by so much expectation. If all goes well, and film one is a success, it represents the start of a franchise. It is a much-loved adaptation of a YA book series with hordes of young fans. But Branagh, who knows his way around a popcorn blockbuster, could be considered a safe pair of hands. He's appeared in one as an actor ('Harry Potter and the Chamber of Secrets') and has directed a few more ('Thor', 'Cinderella', 'Jack Ryan: Shadow Recruit').

Still, it is, even for a director of his standing, a plum job. He was drawn to the world of Artemis Fowl he says because of "the imagination, it felt very original. I loved it's Irishness", which he connected with especially as someone who comes "from the North part of that country". He enjoyed too, "the collisions... the proximity of worlds, very different worlds. I like that creatively. It always feels like it's a good risky place to be. I had some experience with it making the film of Thor, where a very contemporary feeling, still heightened world of science is right next door to a world of magic. So the way those two things inter-relate has always been very fascinating to me".

In 'Fowl', the action shifts between Ireland, Haven City, (a subterranean fairy world) and Ho Chi Minh City, to name just a few places. These shifts, Branagh explains, "mean you can be poetic, it means you can have a size that does invite a big audience to go to the movies to watch it on a big screen with a lot of other people because somehow the subject matter expands away from the norms".

Perhaps surprisingly, Branagh cites 'The Godfather' as an influence for his take on the Artemis origin story, in which the young protagonist experiences something of a loss of innocence as he learns of his complex family history and the dark dealings therein.

"I always look at the masters, the great classics," Branagh says. "Don't take this too literally," he says, but a "story shape that I found interesting as we were considering this was 'The Godfather', where Michael Corleone, as you may recall at the beginning of the first film, although part of a family he knows to be involved in business, he's been in the services and he's not entirely aware of exactly what dad does, and I think that Artemis has, but by the end of the picture he has to face up to, well shall I do some of this as well, do I believe in it? Am I behind it?"

Two young Irish actors will star as the main characters, Artemis, and the fairy Holly Short, in a piece of casting that will almost certainly change their lives.

Lara McDonnell, who will play Holly has some experience of showbiz, (she played Matilda in the 'West End' between 2015 and 2016) But for Ferdia Shaw, the 11-year-old Kilkenny boy who was cast from an open call, it's an entry to a new world as startlingly different and fantasy-like as Haven City.

"With Artemis and with Holly... we looked at literally hundreds, in fact thousands of people to find what we thought were the right characteristics," explains Branagh.

For Artemis they leaned towards casting an Irish boy from the first. "We saw probably 1,200 boys. Anyone from Ireland who applied, but people from all over the world, absolutely all over the world. A tough one was people from other cultures or backgrounds doing an Irish accent. It's tough at the best of times. There's so many of them, as there is in any nation there's always a trillion accents - there isn't a single one. But there is always a little cultural frisson that you get out of - in his case he comes from Kilkenny. And Lara McDonnell plays Holly, who is part of a fairy world that appears to be underneath Ireland, so she also happens to be Irish. That helps, I think, locate something quite distinct in the tone of the movie. We hear the accent so much that it feels as though we just really are in another place."

Lara and Ferdia will join an all-star cast that includes Dame Judi Dench, cast as fairy police chief Commander Root, and Josh Gad, who will play "kleptomaniacal dwarf" Mulch Diggums.

"What I knew was he (Gad) was a joy to work with as indeed is Judy Dench. I'd met him before but it was the first-time experience working with him. But certainly, I knew that because he was Irish in spirit that a certain kind of fringe of anarchy would be in the movie."

There will also be a brief stint of filming in Ireland. "I think often even for a short time, the spirit of a place, even for a few days if you are in a different place... there's a different sense and vibration. From its very authenticity," he says.

"We went to Ho Chi Minh City to shoot at the beginning. Ferdia and Nonso (Anozie, who plays Butler) who had never been before, were travelling around on mopeds... safely, safely! No children were exposed to any form of possible health and safety implication in the carefully orchestrated thing," he is at pains to point out.

"But it was an incredible culture shock - the noise, the traffic, particularly motorcycle and moped traffic, the friendliness of the people, the curiosity of the people and all of that is an incredible sort of injection into the beginning of the movie."

The same principle applied for shooting in Ireland.

"The sea and the Atlantic coast... I always think it when I fly home, there is a green that, there's no other colour but that Irish green. It sounds like a bit of a sentimental thing to say but that's always how I feel about it, so if that's in the movie I think that's a good thing."

Artemis Fowl opens in August 2019