Kenneth Branagh's nephews inspired him to take on the movie adaptation of Artemis Fowl after raving about Eoin Colfer's book series on vacation.

The actor-turned-director was so taken by the kids' response to their holiday reading choice he decided to pick up the books for himself, and then discovered he was a studio front runner to take the stories to the big screen.

"Artemis Fowl has been something I've been developing for three years now," the Brit tells Entertainment Tonight. "My nephews were both reading Artemis Fowl four years ago. We were all on holiday together and they said, 'You should have a look at this', and I did.

"Then, about three weeks later, Sean Bailey (from Disney) rang up and said, 'Have you ever heard of Artemis Fowl?' I said, 'I just read the first book!' There'd been some scripts and versions and developments up to that point, and they said, 'Would you be interested in taking it on?'"

The film reunites Branagh with fellow Brit Dame Judi Dench, who has appeared in several of his films and plays.

The filmmaker actually switched the sex of her character, so she could play Root and he reveals the actress is struggling with the role at times.

"I've worked with her many times now, and it was just something that a great theatre director, Pete Brook, refers to as the 'uninformed hunch'... Whenever I ask Judi to do something, she says, 'Is it different?' The other day... Judi looked a little bit trembly lip. She said, 'I don't know how to play this part', and I said, 'Maybe one of the things is that it sounds quite unlike anything you've ever done, you look quite unlike anyone you've ever looked like - and I knew that would appeal to you'.

"We arranged a meeting and I said, 'So, should we talk about the characters?' And then she started walking around (and) just threw the odd line out... She just started doing this (voice)... Then she turned into this six-year-old and said, 'You think that would be any good?' I said, 'That would be good. That would be really good!'

"I reminded her about this the other day... and she was tickled pink. She said, 'Rehearsals are useful!'"