The documentary-maker’s new series returns to the dark underbelly of the US. But with Trump in the White House, and fringe beliefs on the rise, is weirdness now mainstream? And does he feel scarred by his experiences?

Louis Theroux has got up close and personal with pimps, paedophiles, murderers, neo-Nazis, Afrikaner separatists, religious fanatics, alien-hunters and a range of eccentrics who are often armed, deluded and volatile. They’re not what scares him. “The truth is, the most terrifying experience is when you’re out on location and nothing is happening. That’s the worst,” he says.

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Viewers of his documentaries – he has made more than 60 – know Theroux, now 47, has built a career on stuff happening. His work relies on made-for-TV moments – the visual gag, a shocking confession, an outrageous boast, a poignant or embarrassing revelation – which make you wince or laugh while Theroux himself looks on, his emotions in check, the quizzical outsider.

Nursing an iced coffee in a near-deserted Los Angeles cafe close to his new home, for once interviewee rather than interviewer, he gives a similar look, the eyebrows arching just a bit, when asked about the process of turning these enigmas of human psychology into films.

“The best decision we made as a production team was to trust in the idea of creating relationships with people, and putting myself in situations that were extreme,” says Theroux. “Good things came from that. A sense of roundedness in the contributors and occasionally a sense of drama when I was put in uncomfortable situations, or when the situations spun out of control. Those were always the best moments.”

Viewers will see the Theroux method anew in three BBC2 documentaries, which plumb America’s darker corners: policing, sex trafficking and drug addiction. Shooting began before Donald Trump took office, so they are not intended as Trumpian parables. “The whole genesis was to go back to the US and, if I’m honest, pick some low-hanging fruit. I have a delivery schedule; I’m supposed to make three films a year. I was making them in the UK, which was very rewarding and interesting, but harder to do because of the number of teams chasing smaller pools of stories. So we got a little bit behind.”

It’s a disarming admission – no guff about Tocquevillian exploration. Theroux may be our ambassador to the wild side, an acclaimed cultural Zelig with a huge following who pops up in the oddest places, but he is also a journalist with bosses, quotas, deadlines and endless fretting about the next commission.

Dressed in a T-shirt and jeans, laptop bag at his feet, he seems happy to pull the curtains back – a bit – on what happens behind the camera once his intense relationship with his subjects ends. You wonder if he is scarred – or feels under pressure to profess being scarred – by repeated immersion into damaged, dysfunctional lives. “I sense that people may want to hear that I am suffering psychological consequences. I certainly get asked it a lot. It definitely gets under your skin in ways that are not immediately apparent. I may be distressingly fine with going into the dark worlds and then hopping out again. It’s quite a weird job.” For some reason, I take this as a no and realise only after listening to the tape later that it could be a yes.

It’s odd, interviewing an interviewer, especially one so famous. Theroux knows all the machinations and deflections, innocent or otherwise. And he has been in the public eye so long, a one-man broadcasting brand, you can’t fully disentangle the person from the persona.

It’s easy to see why people open up to him. Affable and solicitous, with brains, poshness and an ego worn lightly, he is a foreigner’s idealised Englishman. He gossips, jokes and cites Max Weber and Jean-Paul Sartre and uses words like “incommensurable”. When you talk, he cups his face in concentration, creating an owlish effect.

Facebook Twitter Pinterest Theroux with Nate Walsh, a heroin user, for his new series. Photograph: Freddie Claire/BBC

Theroux moved from Britain back to Los Angeles, an old stomping ground, in August, and lives in a neighbourhood close to the Hollywood sign and the Scientology headquarters, which he knows from making My Scientology Movie, his first theatrical release, last year. “I’ve always found it easier to work in the States, for various reasons,” he says. The country, after all, is a story factory, even if some, such as last week’s mass shooting in Las Vegas, seem grimly familiar. “I still remember being in America [in 1999] – on location, shooting an episode of Weird Weekends about wrestling – when Columbine happened. Nothing has changed. Americans tend to see these spree shootings as a reason to buy more guns, not fewer. I honestly can’t imagine what it would take to change the paradigm. It’s too deeply ingrained in the myths Americans have about themselves.”

Theroux is working on a long-term project about Trump supporters. Their president (and his – he has US citizenship) is no fool. “Trump saw through so much. For all his awfulness, I can’t but help admire his shamelessness, in an odd way. Or maybe not admire, but be fascinated by it and maybe envy it. In a shame culture he seems to have figured out that if you refuse to be shamed, it gives you enormous power.”

One can only imagine the result if Theroux were to join the president for a golfing weekend at Mar-a-Lago. That The Apprentice propelled Trump to the Oval Office, giving him the nuclear codes and a platform to threaten North Korea with Armageddon via Twitter, is a level of weird not even Theroux’s oeuvre anticipated. In a saturated media landscape what, I ask, can he bring to Trump coverage? “I guess we’ll see. I’ve always been fascinated by fringe beliefs and taboo attitudes, and some of those attitudes are creeping towards the mainstream. At that point, it stops being called weirdness. In a sense, weirdness is a majoritarian phenomenon. If enough people believe it, it stops being weird.”

Theroux was born in Singapore, the son of Anne Castle and the travel writer Paul Theroux. He went to Westminster public school, obtained a first in modern history at Oxford and splashed into television in the early 90s doing offbeat segments for Michael Moore’s TV Nation series. “Michael had a year-zero attitude to TV-making, which was that most TV is shit and we are revolutionaries, and are trying to change the world, and should behave like you’ll never get another job in TV. In other words, scorched earth television. Part of that was helpful.”

Theroux’s method evolved from “trying to extract as much humour from situations as possible” to “trying to enjoy the experience and see what it is that fascinates me about the story”. Everything went smoother once he learned to trust his instincts and not overthink things, he says.

Even so, he felt paralysed with anxiety when the BBC contracted him for Louis Theroux’s Weird Weekends series – a dive into white supremacy, pornography, survivalism and other subcultures. “I was probably, in a pretentious way, thinking that these are more than TV shows … that they needed to take things to the limit in some very undefined way.”

In 2000, he profiled Jimmy Savile, then still a beloved children’s TV presenter. The documentary captured tantalising glimpses of a darker man, but Savile’s long history of child abuse emerged only after his death in 2011. Theroux berated himself for letting Savile off the hook in a sequel last year. Some think he flagellated himself too much and BBC top brass not enough. “I can’t really say whether or not I was too hard on myself. I was just trying to account for my own role in the affair and understand why I wasn’t able to see more.” He remains proud of the original film. “It’s enormously revealing, very hardheaded and journalistic, and explains a lot about his outlook and his weird attitudes.” Theroux stayed in touch with Savile for several years, considering him “slippery and tricky” but also funny and perceptive. One motivation was “hope that he might drop his guard or that I would figure out his secret, whatever that might be”.

Facebook Twitter Pinterest Theroux with Pastor Fred Phelps while filming with the Westboro Baptist Church in 2007 Photograph: BBC

Years later, nagged by guilt over the transient, transactional intimacy between interviewer and interviewee – “you’re in people’s worlds in quite an intense way and then you leave” – he revisited 10 subjects in a book, The Call of the Weird. They welcomed him back, but were puzzled; unsure of the point, he says. “I was romanticising the nature of the connection that I was having on location. The transaction is transparent, [subjects] understand that’s what I’m there for. Maybe I needed to let go a bit more. That was my conclusion.”

His new three-part documentary series – “trilogy sounds a bit pretentious” – shunts Theroux on to terrain with plenty of grey shades and limited light. “I already understood the dark side of the US exists, but this gave me a greater appreciation for the darkness that’s following in the wake of these various phenomena.”

The first in the series, Heroin Town, airing on Sunday night, embeds Theroux in Huntington, West Virginia, where overprescription of painkillers has unleashed a heroin epidemic. Theroux avoided rehab centres – “a bubble where you’re not seeing the seduction of the lifestyle, and you’re hearing these cliches about recovery”. He also largely steered clear of the pharmaceutical companies, regulators and politicians who permitted the disaster. “When money is the motivation, there’s not an awful lot for me to unpick.” Instead, he hung out on streets where heroin and opioid addiction is “off the scale, unlike anything I’d ever seen before”. The addicts, in other words, are the stars. “We give them space to express themselves. There’s a bit of romance that goes with the idea of being filmed. People are able to self-mythologise. And sometimes that’s quite a good thing because it puts people in touch with their own sense of being stars of their own life. Even heroin addicts – there’s a Bonnie-and-Clyde archetype with many of them. While paying lip service to the idea of recovery, you can sense that they’re still beguiled by the romantic idea of what it means to be an outlaw.”

Murder in Milwaukee follows a mostly white police department confronting surging gun violence, homicides and racial tension in a mostly black community. “I have a feeling they assign us the best cops when we’re out on location,” says Theroux. “You spend time with them, you get to like them, so you could argue you’re getting a distorted view.” He sighs. Cops, he says, are better and worse than they’re given credit for. “Rules get bent, sometimes in a way that’s questionable. And other times, if the rules weren’t nudged or massaged the really good work wouldn’t get done.”

Sex Trafficking Houston traces the tangled relationships between sex workers and pimps, some violent and dealing with drug addiction, others not. “You have women with very low self-esteem who come from abusive backgrounds – their circuits are all scrambled.” He avoided the term “sex slave”. “If you overdo the abusive dimension, you strip the women of agency – it’s oddly disempowering and kind of neo-Victorian. The women are getting a kind of emotional fulfilment in their relationship with the pimps, even though it is poisonous and often damaging.” The pimps tended to be stylish, eloquent and intelligent. “These guys are, in their own way, deeply damaged, often the children of prostitutes, who may have had dads or family friends who were pimps. The closest analogy I have is that they are living in semi-apocalyptic conditions where the police are just not an option.”

Theroux has a fourth documentary in the works, about anorexia. Murder, abuse, addiction, disease – it’s a long way from his TV Nation days following Avon ladies up the Amazon river.

How, I wonder, does he process stress? “If I can’t deal with whatever drama is going on, I’ll find myself chopping in the kitchen. I cook things that don’t need to be cooked. I make soup and sauce and freeze it – anything that involves chopping and frying.”

Being Theroux, he has a theory about this. “In this post-feminist era the kitchen has become the place for the man to hide, for masculine disengagement. If I’m chopping an onion, that’s my safe space. I made a huge amount of carrot soup the other day.” He smiles and doesn’t need to say it. Documentaries fill his freezer with soup. Weird.