Interview: Is Karl Pilkington, as Ricky Gervais describes, really the funniest man alive?

The name Karl Pilkington might not be familiar to everyone, but his voice is recognised by millions. Pilkington was for two-and-a-half years Ricky Gervais's producer on the Xfm radio show he presented with his comedy partner Stephen Merchant. Pilkington was originally a producer but gradually became integrated into the show, so taken were Gervais and Merchant with his deadpan, crackpot theories and observations, such as "parrots have gone a bit quiet since pirates have gone".

Gervais has described finding Pilkington as like discovering a magic lamp. "When you rubbed it, magical twaddle came out." The comedian later also described Pilkington as "the funniest man alive in Britain today", but also declared him "an idiot".

The Xfm show was released as a podcast in 2005 and is listed in Guinness World Records for the most downloads: five million in one month. Since then, Pilkington has acquired a fanbase independently of Gervais and Merchant and has his own website. Selected transcripts from the podcasts, illustrated by Pilkington, were turned into a book, published last year, called The World of Karl Pilkington, which was No.1 in the Amazon book charts based on pre-orders alone.

Pilkington mooches into the Oxford Circus café where I'm meeting him, round the corner from where he lives with Suzanne, his girlfriend of 13 years. He is surprisingly tall, wearing a pair of nondescript brown combat trousers, white trainers and a black hooded top. Photos often make him look hopelessly slack-jawed and dim, but in person he looks perfectly normal, although his head, which Gervais has frequently marvelled at, definitely looks a little bit big for the rest of his body. His fleshy moon-face looks like a great, worried, hairy cheese. When he smiles, which he doesn't do often, he has dimples and very large, even teeth.

Despite this unpromising appearance, Pilkington's new project, where he appears on camera, reveals that he is a natural on television. He has already done time behind the camera, making four short documentaries for the Channel 4 series Three Minute Wonders. But he recently made a half-hour documentary for the annual Channel 4 series Comedy Lab, called Satisfied Fool. In it, Pilkington goes to visit so-called "intelligent people" (Will Self, Germaine Greer, David Icke, Professor Heinz Wolff) to find out whether, if he were more intelligent, he'd be happier.

Not that he's unhappy, he says. Nevertheless off he trotted to see Greer, who baked him a loaf of bread, Self, who threw him out of the house for saying that all he wanted was to be a "slightly happier pig", and Wolff, who got upset because Pilkington started talking about aliens.

Pilkington liked all of them. "I would never slag any of them off because they all agreed to do it and it was good of them." Icke made the best impression on Pilkington, mostly because he was nice, not patronising, and gave him some herbal tablets that helped his kidney trouble. Pilkington wanted Brian Sewell to do the programme, but he wouldn't. "He nearly did it but then he didn't. I think he thought it was a wind-up or something. But why would I do that? What's the point?"

Watching the programme, you can see how people might think it was a wind-up. There are a couple of Ali-G-esque moments, when Pilkington says something so ill-educated or naive that Greer, Wolff and Self get a look on their faces that seems to say, "Oh God, am I being stitched up?" Icke, to his credit, takes it all in his stride. He just says: "Oh, if people think you're stupid just say bollocks to the lot of them."

Pilkington's other new project is a book called Happy Slapped by a Jellyfish. It is a series of musings about holidays he's had. "Not to really exotic places. Just, you know, Ibiza, Tunisia, the Cotswolds and stuff. I'm not Michael Palin." On pre-sales alone, it is in Amazon.co.uk's Hot 100. "It will no doubt be one of the strongest-selling comedy titles this Christmas," says Kes Nielsen of Amazon.

With his soothing, methodical, plodding way of describing things and sharp eye for odd, significant details, Pilkington is not unlike Alan Bennett. He brightens at this comparison. "Oh, yeah, Ricky said that, too – that the Jellyfish book was a bit like that one Bennett did. That stories one. I've not read it yet, though. The reason I did the book about holidays is that you're a different person on holiday. You're sleeping somewhere unfamiliar, knocking about with people you've never met and for 10 days you're someone else. You're out of your comfortable zone."

Pilkington is by no means stupid. But he is mildly neurotic about the things that people are commonly neurotic about – time and space; he dislikes being late and is fastidious about deadlines. He also gently frets about whether there is enough space on the planet, at how many people there are, at the number of insects there are, and at how with his new book he might be taking up someone else's "space" on the shelves in the bookshop.

He is not hilarious. But he is amusing, absolutely, and very good at telling stories, such as one about builders that made me laugh out loud: "There's work going on in the downstairs flat and the builders are Polish and so they work longer hours than any other kind of builder. So they start at 7am and go on until 8pm and it's really noisy. And they've been at it for three months. I don't know what they're doing. What can they be doing? It gets you down after a while, it does your head in. But they're quite like that, builders. I had some in a while ago and they'd wind me up, asking what the pub across the road was like and I was thinking, 'What? You're not here to go to the pub, you're here to do a job.' And one day they came in with a big bag of papers and magazines and a Pot Noodle, as if they'd just come to my flat for a read."

But I'm not constantly in stitches. So why does Gervais think he's the funniest man he knows, then? "Comedy's really subjective, you know," says Pilkington, "that's why it's so hard." Most of the comedy from the famous podcasts comes from Gervais and Merchant being mercilessly unkind to Pilkington, refusing to humour any of his slightly crackpot theories about population control and snapping at him ("I saw a similar sort of theory written out on a wall, but it was written in shit"). If you don't think that bullying guileless people is funny, then Pilkington, by himself, is not a comic genius.

But that's not to say that he isn't good company. And he makes excellent television, with his bemused, furrowed little brow and flat, Mancunian vowels. He is soothing and comforting in his plain-speaking seeking of answers, although he also frets that he isn't a "proper presenter".

"I emailed Will Self to see if he'd he would play pool or a game of Scrabble or something, because I'm not sure how I'd do a formal interview and he sent back an email with a quote saying, 'Games are just for people who...' something, something, something... And I just thought: 'Yeah, OK, but can we play Scrabble or not?'"

Pilkington's ultimate ambition is to make David-Attenborough-style programmes about insects. He's under no illusion that he's a comedian and he sweetly and modestly expects all this independent success to come crashing down at any minute.

"If you'd have told me five years ago that I'd have done all this – two books, some television and everything – I'd panic, I'd be scared. And you never know, this might all be over soon and I'll look back and think: 'Well, that was all a bit weird, but never mind, it's nine o'clock. Got to get up and pack them boxes.'"

Happy Slapped by a Jellyfish is published by Dorling Kindersley at £12.99. Karl Pilkington: Satisfied Fool will be screened on Channel 4 on 22 October