Karl Urban has been an integral part of some of the biggest movie franchises of the past few years.

He played Eomer, one of Aragorn's pivotal allies, in two Lord of the Rings movies; ruthless assassin Kirill in The Bourne Supremacy; and, most recently, Dr Leonard "Bones" McCoy in JJ Abrams' Star Trek reboot.

Now he's the focal point of another potential franchise in Dredd, playing the helmeted lawman of 2000AD's violent comic book series. It's unfortunate, then, that you don't get to see his face.

But the New Zealand-born actor was never about to let vanity take over and fall into the same trap that turned fans against Judge Dredd's previous movie incarnation, 1995's much maligned Sylvester Stallone vehicle. Rather, he embraced the challenge of letting his chin take the lead.

"I didn't consider that at all because, to me, character acting is how you do what you do," he told me when we met to discuss the film in London.

"Yes, you don't see my eyes, but you hear my voice and the physicality of the character takes on a heightened significance. It was an amazing challenge, but I learned to have faith in the fact that if you think the thought and feel the emotion, then the audience will too."

For Urban, the key to a successful Dredd film was always about remaining faithful to the comic books and British writer John Wagner's original vision. And by doing so, he feels the fans are in for a treat.

"It's the one they've deserved for the last 35 years," he says.

For the uninitiated, Dredd is set in a violent American future where the east coast from Boston to Washington has been turned into one giant metropolis known as Mega-City One, where cops known as judges preside over the lawless streets serving as judge, jury and executioner.

Urban first fell in love with the character at the age of 16 while working in a pizza parlour, still harbouring dreams of becoming a successful actor.

"I just responded to this cool, enigmatic lawman," he recalls. "I loved the dry humour in it. I loved the characters within Mega-City One and the morality tales that were quite often told.

"I loved the science fiction element of it as well, having been a big fan of movies like Blade Runner, Alien and Star Wars.

"And I guess I enjoyed the escapist element of the sort of futuristic vision. Really, Dredd in its early incarnations was a response to Thatcherism and I liked how it explored freedoms that you and I take for granted and things that would seem so preposterous, like sugar being legal. In Dredd's world, it's illegal. So, that was interesting."

Did he dare consider actually playing Dredd at that point? "No, I've never really been like that. As a young fella watching those characters or reading the comics, it's not natural to think 'I'm going to do that one day'."

It's quickly clear from speaking to Urban that he's a realist who likes to keep himself grounded. He's had to work had to get where he is today and he takes nothing for granted.

"Coming from New Zealand, it seems like such a distant, impossible dream to have," he replies when I ask how tough his journey to leading man status has been. "But through a certain degree of perseverance I've just sort of stuck in there. And I've been really blessed to have worked with some of the best directors in the world [including Peter Jackson and Paul Greengrass] and some of the most amazing actors. So, I've watched them and learned from them."

Having made it, however, the 40-year-old is also determined not to turn his back on his roots and continues to live in New Zealand with his wife and two sons.

"That's where I want to raise my family and it's where my family lives. It's culturally what grounds me. I couldn't conceive of permanently living somewhere else. But one of the cool things about my job is that I get to go and live in different parts of the world for three or four months while I make a film."

For Dredd, this involved living in Cape Town, South Africa, where he was able to focus on inhabiting his character, from helmet and uniform right down to voice and mindset.

"I actually put that uniform on a full two weeks before we started shooting. I wore it every day just to get used to it because I wanted it to feel like a second skin. And it took some getting used to!"

But it helped when tackling Dredd's ability to be mobile and fight whatever blocks his path – in the film's case a tower block full of villains led by Lena Headey's sadistic, drug-dealing murderer Ma-Ma.

Urban even went through a rigorous boot camp. "I worked with an ex-British military lot and they taught us [he and co-star Olivia Thirlby] weapon safety, how to move through spaces and how to clear spaces.

"We even went so far as to have mock-ups of the Law Giver that contained a BB gun inside. And we went through live firing exercises with the stunt team where we would literally be getting into fire-fights with the stunt team.

"They would be secretly deposited through the set and we would have to go and clear the set as a team. And we'd be firing at each other. It was as close to reality as I would ever like to get."

And then came the voice and his lack of verbosity. For the former, Urban drew from the comics and a note that described Dredd's voice as "like a saw cutting through bone".

In terms of Alex Garland's script, he took the less-is-more approach of his character to interesting new extremes.

"When I got the script, I went through it and put these big lines through Dredd's dialogue. If it took too many words to say it, I cut a line through it. And when I opened up my script for a script meeting we had, Alex sort of saw the lines and enquired about them. And I said: "I love this dialogue but Dredd says less!" And he replied: "Oh, that's funny... that's exactly what [John] Wagner said."

Given the amount of work put in, Urban says he would love a second chance to play the character but – like everything in his life – he isn't expecting to or pinning his hopes on it. And besides, he's also busy with other projects, including playing Bones again for next year's Star Trek sequel (which was "a lot of fun") and a remake of Belgian thriller The Loft.

"Don't get me wrong, I would love the opportunity to play Dredd again," he concludes. "But the type of guy I am, I just don't like to get ahead of myself. I like to live in the moment and not live in the vacuum of expectation. I just really want to enjoy the fact that, hey, we've made a really cool film and the rest is beyond my area of concern."

Dredd opens in cinemas tomorrow