We meet at a café in Islington. Louis is 35, well over 6ft tall, with dark, blinking puppy eyes. He isn't a snazzy dresser, exactly. He is wearing a black, cable-knit sweater which I know is from Gap because the label is sticking out the back. His feet are encased in what appear to be jumbo-sized versions of the black, untrendy shoes that boys who suffer compulsory school uniform are forced to wear, and even then they'll rarely succumb without protest.
Still, he was once voted seventh most-wanted single man in Tatler - how I wish he could see me at breakfast! - although I think it's less to do with "out there" sexiness and more to do with his air of "at sea" vulnerability. How I long to tuck that label in. How I also long to go back to his place, although possibly less to give him a good going over than to give his sock drawer one. I note his specs have been endearingly Jack Duckworth-ed with Sellotape.
"I tried to get them fixed a week ago," he says, "and I'm very annoyed about it." Specsavers, he continues, said they could get him a new arm bit before his appearance on the Jonathan Ross show, but they didn't. "So I put the tape over it, then coloured it black with a felt pen. I think I got away with it."
I don't think it would occur to him to just buy new glasses and have done with it. "Do I care about clothes and stuff? Not much. It's a bit sick, isn't it, people spending all that money on clothes? I'm too stingy. I wouldn't pay £100 for a shirt."
Have you ever been really, shamingly, extravagant? He has a long think. The puppy eyes blink. "I recently," he finally announces, " splashed out on this box set of videos by directors Chris Cunningham and Spike Jonze. It was probably £20." I affect to look aghast - as if I could never imagine spending a whole £20 on anything - but possibly fail, as he then ups the ante. He adds that, because of the Jonathan Ross business, he spent £50 on a haircut in a smart salon. "I'm getting a good reaction to it, though. By degrees, we are corrupted inch by inch."
We are here, ostensibly, to discuss his book, The Call of the Weird, a sort of follow-up to his TV show Weird Weekends, in which he revisits many of his original subjects: the UFO believers, porn stars, neo-Nazis and the very, very scary April Gaede, the white supremacist stage-mother-from-hell who has turned her twin daughters into a Hitler Youth version of the Olsen sisters, singing sweetly about terrible Aryan things to stiff-armed salutes. April has since had a baby boy, Dresden.
On the revisit, when the kids ask what's for lunch, April says: "We could always stick a Jew in the oven!" I tell Louis that, even though I am the phoniest, most craven person ever - that I will, for example, happily tell someone like Edwina Currie that I adored her latest novel even though it was so bad I couldn't get beyond the first page - I'm not sure I could go along with a remark like that. Do you never recoil? Don't you ever think, nope, this time there really isn't a shred of common ground?
He says: "You know, I don't worry about it over much. I don't feel that as human beings we have an obligation to dislike someone based on their beliefs, and it's OK to have a human reaction to someone even if you feel what they do is hideous and objectionable. You can still enjoy their company and find them interesting to be around."
He adds that these people are so on the fringes, so far from where real power is, that they don't really matter. I say, true enough, for now, but a fringe can quickly build into a movement and then we've all had it. Jews did get put in ovens, after all. He says: "The trouble is, I just don't know if I'm too human or not human enough." I think I understand. What does it make you, if you can see the good in the bad? And who can say?
Of course, at some level, he has to keep his subject on side, has to go along with whatever vision they have of themselves, otherwise he wouldn't have a TV show or book at the end of it, just as I have to keep Louis on side, or I won't have enough words to fill this space. ("Great haircut! I think you did get away with the taped glasses! A basque to breakfast! Just fancy!")
He is often accused of being a faux naïf, a phoney innocent, playing a game of seduction and betrayal, seducing with that faintly apologetic air of Hugh Grant-ish puzzlement, betraying with what is obviously a killer mind. (He has a first from Oxford, which does it for me).
Any truth in this? "I don't mind when people say that, because it's kind of a compliment in a way. People are crediting me with a level of forethought I don't posses." His claim that he is not disingenuous might in itself be disingenuous, but who cares? His gift for the awkward exposé might even lie in this very ambiguity.
As for what is real or phoney, "it's a false choice. We all have equivocations. Interestingly, Ann Widdecombe once said to me, 'Everyone should have some belief that they should be willing to be burnt at the stake for.' At the time, I was like, maybe so, but I'm no longer sure. There is no shame is being ambivalent about almost everything in your life."
He thinks, by the way, that his Ann Widdecombe profile worked the least well of all the When Louis Met... programmes. "I think she felt she'd signed up to something she didn't want to be part of. She enjoys being on TV, but she doesn't enjoy revealing herself. One of the biggest misconceptions about her is that she is somehow sexless. She won't appreciate me saying this, but my impression of her is that she has a carnal side to her that she is afraid of.
"She's certainly very different around attractive men. My executive producer at the time was an impressive figure and I saw her when she was with him, and she kind of melted." As Christine Hamilton did, when she all but sat on your lap? Still, he did put the killer question of the day to her: "How do you make your hair look more real, Christine?"
His father is Paul Theroux, the novelist and travel writer, so I wonder if Louis always thought he would write a book. Yes, he says, he did. "I always grew up with an assumption that I would be a writer. It was like taking over the family pub."
He first properly encountered his father's writing when he was 11 or so and read Mosquito Coast one day when he was off school sick. "I really did think it was an incredibly powerful book and I couldn't quite believe that my dad had written it." At one point, David Bowie optioned it, which was hugely exciting. "I was into Bowie and everyone at school [Westminster] was into Bowie, so I went and told them, and I thought it would make me the most popular boy in school, but if anything, it made me rather unpopular."
Bowie was my first crush, I say. He says his was Babs in Pan's People, if you don't count "my teacher at my primary school in Wandsworth. When she'd bend down to help with your work you'd try to see if you could look down her blouse." He accepts that his observational techniques have grown a little more subtle.
Did you, I ask, learn things about your father through his books? " Definitely." What? "Um... I suppose I realised that my dad had a Catholic upbringing and, whether or not because of that, it's always a struggle with relationships - and that comes out very strongly." What kind of struggles? "Um... being monogamous." Ah. His parents divorced in 1993. A shock, Louis? "When it happened, yeah. I didn't expect it. It didn't shake my world, but it shook my view of my family. Perhaps my family was less happy than I'd thought."
He now lives with his girlfriend of three years, Nancy. He is better now, he says, at relationships than he used to be, thanks to eight months of cognitive behavioural therapy. I naturally wonder what took him there. " There'd been two relationships that didn't end very well, so I thought this is perhaps something I can chat to someone about. It's not voodoo. I think it was quite helpful." In what way? "OK, here's my thing. Sometimes I get overconcerned about things and over-react. If something is not going well, it's like, 'Fuck it, it's not working, I'll do something else.' Instead of looking at the intermediate steps I can take, I'll hit the nuclear button." He then says he doesn't want to go too far down this road. "It's all a bit touchy-feely."
I can tell he is torn between giving me what I might want and keeping to himself what he doesn't wish to give. Paradoxical, for a professional interviewer? No. Sensible, I would say. As it is, I wish I hadn't mentioned the bloody basque.
So what do I find out? He can cook, poorly by the sound of it as he relies a lot on tinned tuna and frozen peas. He likes films, music, tennis and Frisbee. He wishes he'd written Truman Capote's In Cold Blood. He might move into covering true crime cases. He doesn't think he'll do more celebrity exposés. They don't need him, now they can get exposure on their own terms through reality TV. He frets a lot about his work and his own motivation. He finds he often wants his subjects to like him more than they ever wish to be liked by him. "He's a neo-Nazi. Why would I even want him to like me? But I do." I like him. I hope we meet again, but preferably not at breakfast.
'The Call of the Weird' is published by Macmillan (£17.99) for the special price of £16.50 (with free p&p), call Independent Books Direct on 08700 798 897