Charlie's intrepid adventures

Charlie Hunnam is recalling a time when he embarked on a camping trip - sans mobile phone - with his long-term girlfriend, jewellery designer Morgana McNelis.

"We went into a big wilderness area in California called Kings Canyon," begins the actor, 36. "I didn't take my phone with me and she kept saying, 'Oh it's going to be so romantic', and I said, 'It's not romantic, it's adventure, it's survival'.

"We were going out into the wilderness for seven days," he reports, animatedly. "And just three days in, we got horribly lost - and were completely lost for four days!

"I was feeling fairly confident two days in; by the third day I started to panic a little bit, and by the fourth, having no idea where we were and seeing no trace of humanity, I started to think, 'Maybe I should have brought my mobile phone...'."

Holed up in a hotel room, Hunnam - best known as the fearless Jax Teller in the hit FX series Sons Of Anarchy - isn't casually reeling off past misadventures.

His admission is in light of his latest role in director James Gray's stirring big-screen tribute, The Lost City Of Z.

Swapping his motorbike leathers for camo chic, he leads the incredible true story of British explorer Percy Fawcett, who journeyed into the Amazon at the dawn of the 20th century and discovered evidence of a previously unknown, and advanced, civilisation.

Despite being ridiculed by the scientific establishment, the adventurer - supported by his devoted wife (Sienna Miller), son (Tom Holland) and aide-de-camp (Robert Pattinson) - returned time and again to his beloved jungle in an attempt to prove his case, culminating in his mysterious disappearance in 1925.

Epically scaled and multifaceted, the drama - based on David Grann's non-fiction bestseller of the same name - provided the change of pace Hunnam needed.

"I've been really lucky, particularly in the last few years, that I've been getting offered lots of diverse and really interesting things," notes the actor, whose previous credits include Guillermo del Toro's films Pacific Rim and Crimson Peak (and he also famously backed out of playing BDSM heart-throb Christian Grey in the film adaptation of 50 Shades Of Grey).

"But more than specifically looking for an adventure story per se, I was eager to work with a high-level director and work on a character that was really complex," Hunnam adds.

"When I read the script, it did strike me as possibly the best opportunity I'd gotten in my career so far. Just because of the depth, sophistication and complexity of what we were trying to say with this film - and the breadth of time period.

"Getting to play 30 years of a man's life was a great challenge," admits Hunnam, whose character starts off in his early-30s but is almost 60 by the end of the movie. "It felt like it was an opportunity to stretch myself and put everything I'd spent 20 years learning as an actor into play."

In particular, the handsome Geordie (his Northern accent barely detectable), who's dressed today in a more practical jeans and blue shirt combo, welcomed the great responsibility of playing a real-life figure.

To prepare, he visited the Royal Geographical Society, where he pored over letters between Fawcett and his wife Nina.

He also insisted on wearing an exact replica of Fawcett's ring.

"There's a museum in Brighton that has some of Fawcett's artefacts," he explains. "They were going to take photographs and create something similar and I said, 'No, no, no, we've gotta go down to the museum and take an impression of the actual ring, make a cast and re-create it in gold'.

"I get a little obsessed about these things, but it's significant for me because Fawcett was wearing this ring when he disappeared," says Hunnam, who lost around 60 pounds for the part. "Several years later, it appeared in a pawn shop, so that obviously added to the mystery."

It's fair to say the voyager's fearlessness rubbed off on him too.

"I loved being there," he says of spending six weeks in Colombia's inhospitable rainforest, despite dishing the details of a hospital trip and course of antibiotics after a beetle bit a hole in his eardrum. "I'm much more fearful walking through Newcastle on a Saturday night at three o'clock in the morning!" he quips, laughing wildly.

A great fan of the outdoors, he adds: "Most of us live in an environment where the most we get to see is a park and a couple of birds in the trees, so to be in a place that was just so filled with life - spiders, snakes, birds, monkeys and caiman and all manner of animals - was a pretty amazing experience."

He's quick to confess he wasn't always so adventurous. "I remember being a kid and being consumed with fear," he divulges. "I was afraid of everything, and I think I've definitely cultivated over many years, a higher threshold for fear."

Hunnam, whose TV career began in children's classic Byker Grove and Channel 4 drama Queer As Folk, is now based in Los Angeles, where he's lived since relocating 17 years ago.

"You know, I missed it [the UK] for a long time, when I was sort of married to LA while I was doing a TV show [Sons Of Anarchy]," he confides. "Now I spend probably about a third of my time here, but I prefer being here on my own time [not working], when I get to see my friends and my family."

Next up, Hunnam will star in Michael Noer's remake of 1973 American prison film, Papillon, plus Guy Ritchie's epic adventure-drama King Arthur: Legend Of The Sword, in which he plays the titular lead, released in May.

While he has no reservations embarking on more action roles, with past (camping) escapades in mind, will his girlfriend have something to say?

"She worries because she knows I can get a bit crazy and put myself into situations that I'm probably often not equipped to handle," Hunnam admits with a smile.

"But I usually find my way through. And I'm still alive, so..."

• The Lost City Of Z opens in cinemas on Friday, March 24