Even the most banal phrases have their uses, and when it came to Bart Layton’s documentary “The Imposter” earlier this year, it’s easy to understand why so many critics reached for that fusty standby: “The truth is stranger than fiction.” Then again, “The Imposter” – one of 15 shortlisted films vying for an Oscar nod in the Best Documentary Feature category – tells a story that is stranger even than most truths.

Centered on the charismatic, frightening figure of Frédéric Bourdin a shapeshifting con artist and serial identity thief who claim to have masqueraded as over 500 people in his lifetime, the film peels back the covers on the Frenchman’s most infamous and improbable stunt. In 1997, aged 23, he seemingly duped a Texan family into accepting him as their teenaged son who had gone missing three years previously – despite not sharing his accent, appearance or even eye color. Turning up in Spain and claiming to have been kidnapped by a military-run child prostitution ring, Bourdin sold his outlandish tale not only to the Barclay family but to the US authorities, and maintained the charade for five months before the FBI caught wise.

It’s irresistible material for any movie – non-fiction or otherwise – and it’s easy to see why Layton, a young, London-born documentarian previously best known for the UK television series “Banged Up Abroad,” was drawn to it for his first feature film. Layton first encountered the story by chance, while flipping through a magazine at a friend’s house in Spain; he knew he wanted to do something with it, but didn’t quite know what.

“I kind of made a note and didn’t find the note again for some time,” he says. “When I got back to it, I felt pretty sure it must have been made into a film – either as a documentary or as a fictionalized version – and was astonished to find that it hadn’t.”

He’s speaking over the phone from Los Angeles, where he’s been put to hard work on the Oscar campaign trail – not that he’s had much of a moment to breathe since the film’s buzz-making debut at the Sundance Film Festival 11 months ago. Even this interview is our second: in the summer, I hosted a Channel 4 Q&A with the director in our mutual hometown, and if he’s grown at all weary of discussing the film in the intervening months, he doesn’t sound it.

After reading up further on Bourdin’s story, notably via David Grann’s extensive 2008 profile in The New Yorker, Layton got in touch directly with the so-called Chameleon through his Bourdin’s YouTube account, and invited him to London to discuss a potential collaboration. “At that point,” Layton says, “I didn’t exactly know what the film would be about – whether it would just be about him, or use his story as a way into something bigger. Which is what we ended up doing.” The attention-grabbing result is an unusual hybrid documentary, remarkably securing the on-camera participation of both Bourdin and the Barclays, but blending their testimonies with stylized, suspenseful dramatizations that evoke film noir more than cinema vérité.

“I never really considered making it as a narrative film,” he explains. “But that’s such a strange term in the first place: aren’t all documentaries narrative?” That’s just as well, since after Layton began work on “The Imposter,” a little-seen, faintly fictionalized film of the story, with a cast including Famke Janssen and Ellen Barkin, was released in 2010; it’s not much of a match for Layton’s take.

“I felt all along that it’s such an unusual and extraordinary story that if you fictionalized it at all, it would seem completely preposterous,” he says. “You wouldn’t believe it. Listening to the people involved telling their stories, it did feel at times like you were listening to the plot of a Coen Brothers film, and I wanted the film I made to have a foot in both camps. Clearly it’s a documentary, with real people, and we were journalistically rigorous about keeping to the details of the case as we understood them. But it was always my intention for the film to play to an audience that might not normally go to see a documentary in the cinema.”

Layton, therefore, has no issue with people describing his film as a thriller – a fragile sense of mystery was key to the filmmaking process. “While making it that I felt we were inside our own detective novel in some ways,” he laughs. “We ourselves experienced a lot of twists and turns along the way. You’d have a conversation one day with a member of the Barclay family and come away convinced of one conclusion, and the next day talk to the FBI, and come away equally convinced of the opposite. So while making the film, our sympathies were swinging to different extremes, and that was something that I really tried to reflect in the way the story was told.”

The audience, too, will feel torn between Bourdin’s cool, calm, vaguely amused-sounding retelling of events and the more stricken accounts of various members of the Barclay family as they struggle to explain just how they were so absurdly fooled. Between them, it’s all too easy to believe the more sinister theories that suggest the family played along with the deception to cover the nastier truth about their son’s disappearance, but this slippery even-handed film never takes sides. Getting the perspectives of all involved parties is essential in this regard, but it wasn’t easy to do.

“Frédéric ‘s not a retiring type, as you can see,” Layton says, “but for someone who’s pretty untrustworthy, he’s also very untrusting. He was very circumspect about the whole thing, but at the same time he was very attracted to the idea of telling his story to an audience. He himself has said that he gets confused between attention and affection.”

Similarly cagey were the Barclays, who hadn’t come out well in much of the media coverage of the story – including the aforementioned New Yorker piece – but wanted an opportunity to tell their side of things to a larger audience. “I think you could argue that they don’t come out of the documentary brilliantly either,” Layton admits. “But there were things they felt they’d never had the chance to express, and they got to do so here. I was nervous about their reaction to the film, but they said it was an honest account of what they experienced and that they were ultimately glad they’d taken part.”

Layton wound up with several versions of events, and found parsing them on screen without emphasising one over the other “a difficult line to tread.” It was important to him that the film not arrive at a theoretical conclusion: “That may be frustrating for some viewers, but life isn’t like a Hollywood narrative – things aren’t nicely tied up. Truth can be a subjective thing in some ways. We believe what we choose to believe. A story we think is about deception is equally about self-deception.

“I had done a lot of research into the case, but that was very different from the experience of sitting opposite a person and hearing the story directly from them. You can’t be prepared for that. It’s an emotional experience in a way that reading an article or file is not. Our natural tendency as human beings is to believe what we are confronted with, but they can’t all be correct.”

Layton found the film’s dramatized sections, slickly shot and infused with a range of Hollywood genre elements, crucial in maintaining the possibility of multiple truths; where most documentary filmmaking is at pains to stress authenticity above all else, “The Imposter” quite deliberately courts fabrication. For that reason, the director is keen to avoid the word “reconstruction,” preferring to think of these sequences as interpretive.

“It’s a pretty dirty word in TV, let alone in documentary cinema,” he says. “It implies forensically reconstructing a series of events that must have happened a certain way – and what we have here is a number of different subjective accounts of the events. For me, the way to depict that was to create a language for film that makes it clear that we’re not telling you what happened. We’re giving you interpretations, or illustrations, of the stories we’ve been told. The filmmaking is an extension of the storytelling: if a great storyteller tells you a great story, or even if you listen to a radio play, you’re going to have a visual impression of it, a movie playing in your head. That’s what I was trying to get at. It’s not supposed to look like fake archive material. It’s supposed to clearly convey that you’re inhabiting their version of a story.”

As such, Layton is one of a growing breed of documentary filmmakers who are willing to play with conventions of form and perspective to most effectively frame his subject and engage his audience. “Of course there are lines that shouldn’t be crossed, and where drama in documentary gets problematic is when the filmmaker is trying to convince the audience that they’re watching something they’re not: that it’s reality rather than recreation. At no point were we trying to pull the wool over the audience’s eyes, though” – he pauses a second, audibly smiling – “one could argue that Frédéric was.”

Layton sees the film’s box office success – it’s the highest-grossing documentary of the year in the UK – as indicative of wider acceptance of a new grammar in documentary filmmaking. The same goes for its shortlisting by the Academy’s often conservative documentary committee, which he wasn’t expecting. Noting the strength and diversity of the shortlist – he describes the competition as “daunting,” singling out “Searching for Sugar Man” as a “great crowdpleaser and a really well-made film” – he describes it as a testament to changed perceptions of what the documentary form can achieve.

“It can offer the same extraordinary, emotional experience that we demand from all cinema,” he insists. “There’s no reason why fiction should have exclusive rights to drama and suspense.”