They are, fairly obviously, not questions that trouble the vast majority of us: Does Finland exist? Is the Earth really flat? Where is the US government hiding aliens? But, as Dom Joly attests, a significant number of people spend an inordinate amount of time pondering such mysteries, often online.

And the comedian turned travel writer now counts himself among them, for purely scientific reasons you understand. His side-splittingly funny new book, The Conspiracy Tourist, investigates this strange and disturbing world. It’s a total hoot from page one but, as Joly warns, the rise of the conspiracy theorist comes amid a decline of public trust in science-based facts and institutions. And that’s something we ignore at our peril.

“No one’s saying governments and corporations haven’t done terrible things, haven’t been a***holes,” he says when we meet. “But everyone seems to get the wrong end of the stick, to the extent that doctors are the new bad guys. I mean, come on…!”

It was Joly’s growing anger at the anti-vaccine, anti-science lobby going viral on social media during the pandemic that inspired the new book. “All through lockdown I found myself online, like everyone, and arguing more and more – especially with anti-vaxxers,” he explains. “And it really p***ed me off because I had a very good friend in hospital on a ventilator, and these f***ers were saying the Covid virus didn’t exist. So I’d argue with them constantly.”

For many conspiracy lovers, it turns out, the global pandemic proved ground zero.

Hoaxes, counterfactual claims and general wackiness went into overdrive, hyped by computer algorithms and cynical social media companies. And the truth certainly wasn’t helped by the likes of Donald Trump and his “alternative facts”.

Anyway, it set Joly off on a global road-trip – to Finland first, naturally, of which more shortly; then Roswell, New Mexico, searching for aliens; Newfoundland; and even Glastonbury – to test the theories and meet some of the folk he’d been arguing with online. Joly continues: “I thought, ‘Do these people really believe it? Or are they doing it just to get clicks, just to be shocking?’ So I really wanted to look them in the eye and say, ‘Do you genuinely believe this?’ If you do, that’s really interesting, or do you just not give a f***?’

One of the greatest, certainly the strangest, examples is the idea Finland, the country, doesn’t actually exist. Joly’s research led him to a long-lost post on internet site Reddit where people shared the weirdest things their parents had taught them.

A contributor called Jack claimed he’d been told the country had been “fabricated” in 1918 by Japan and Russia so they could exploit the fish stocks in that part of the Baltic Sea. He didn’t believe it himself but… And, after that, people suddenly started doubting the existence of Finland (population 5.6million).

Travelling to Finland with his Canadian wife Stacey, who tells him it’s the dumbest thing she’s ever heard, Joly admits: “I was 99.9 per cent sure she was right but, if I was to take a proper look at conspiracy theories, then I needed to open my mind, discard my lifetime of institutional brainwashing and embrace everything.”

Today he adds: “It’s a classic example of how conspiracies often start as a joke.”

You’ll have to read his book to discover whether Finland does, in fact, exist but (spoiler) the Jolys did visit Finnish capital Helsinki – or at least so he claims!

Another classic is modern flat-Earthism which was reignited by a couple of stoned US academics trying to come up with the maddest idea possible. Incredibly, it’s now split into two factions: those who believe the Earth is a disc, and so-called “square” flat-Earthers,

“They’re a splinter group who believe the Earth has four corners; Hydra in Greece, the Bermuda Triangle, Papua New Guinea, and an island called Fogo in Newfoundland,” Joly says. “So I went to Fogo and I found a square flat-Earther and took him on a road trip to the edge of the world.” Hiring a fishing boat, ostensibly to take them to the “edge”, the man accused Joly and their captain of “going round in circles” when they couldn’t find it.

“He was a really smart guy who somehow got lost down some internet algorithm,” says Joly. “He didn’t want to be proved wrong – because suddenly you’ve had your whole belief system and your whole life questioned.”

Is that why people cling to such strange ideas in the face of reality then?

After all, the Finland and flat-Earth conspiracies might amuse us but, dig deeper into the netherworld and it quickly goes dark: from the idea 5G mobile phone masts caused Covid, to deeply unpleasant claims victims of a brutal US school shooting were child actors, the whole incident staged to promote gun control. “If I learned anything from my travels, it’s that s*** happens,” says Joly. “Life is chaos but, as humans, we don’t like chaos, so we try and make order and conspiracy theories give you that. If terrible things happen, it’s not random, someone’s behind it. It’s not your fault. But it also gives you this secret knowledge and you feel empowered.”

Unsurprisingly, in Joly’s view, the US is the spiritual home of the conspiracy theory.

“It’s a very American thing,” he says. “There’s an anti-elitism, anti-expert feeling in America which comes from mistrust. They’re a rebel nation, born out of revolution and hating ‘the Man’. Most Americans think King George is gonna come smashing in their door. That’s in their DNA, so I think conspiracies particularly appeal to them.

“It’s similar to cults and religions. If you argue with them they just retreat. So you can’t change them. Because they’re obsessed, you can’t possibly have enough facts to out-argue them. It’s like a religion because it becomes your tribe, your identity, it’s very difficult to get out of it.

“Social media is a massive part of it – it gives you a tribe and it feeds you crazy s***. I’m not normally my own quoter, but my favourite line from my book is that, ‘in the old days, every village had an idiot, but now they all join each other’. Before, you kind of kept a bit quiet about these sorts of views. Now they’re emboldened.”

Of Jones in particular, Joly fumes: “Can you imagine anything worse than your tiny kids being shot somewhere like Sandy Hook, then to have people hound you online saying they didn’t actually die? So much so that one of the parents had to move house about 10 times because he got so harassed. And that is coming entirely from people like Alex Jones, who are making s***loads of money off it. It’s just beyond despicable.”

Sadly, he didn’t manage to get face-to-face with Jones, 49, though not from a lack of trying, having doorstepped him.

“I was doing a rubbish Louis Theroux and I suddenly saw Alex Jones in the background and tried to ask him a question,” Joly says.

“Then the guy at the door pulled a handgun and I walked away very fast. You suddenly think, ‘What the f*** am I doing? They could probably legitimately shoot me!’”

Joly, who admits rather sadly he’s unlikely to change minds, finds the suggestion there’s a global conspiracy among the elite especially funny. “I’ve met politicians, I’ve met powerful people, I’ve met journalists,” he chuckles. “None of them could organise a parking system that works, so how can they secretly run the world? Conspiracies about a shadowy elite have given them so much more credit than they deserve.

“But the book wasn’t about trying to change people’s minds and it’s not really a scientific discovery of conspiracies.

“Essentially, it’s a funny romp through a really weird world but, along the way, I do make some serious points.”

Joly has had a fascinating life and career. Born in Beirut in 1967, the son of a British archaeologist, he attended school in Lebanon before completing his education in the UK and reading politics at the University of London. After becoming a star with Trigger Happy TV on Channel 4 – several strangers a day still shout “I’m on the phone,” at him, he admits – he created This Is Dom Joly and World Shut Your Mouth. More recently, he has appeared on reality TV, including I’m A Celebrity, and fronted documentaries. He has two children, Parker, 22, and 19-year-old Jackson, with wife Stacey and lives in the Cotswolds.

The Conspiracy Tourist is a gift of a documentary. Joly, whose previous books include The Dark Tourist – catchlined “sightseeing in the world’s most unlikely holiday destinations” – is hopeful it will come to the small screen. After all, he points out, conspiracies are all around us. As for what we can do about it, he’s not so sure.

“If you think about what’s happening in Gaza, when the [Al-Ahli] hospital was recently hit, the Israelis said it was a Hamas rocket, and Hamas said it was an Israeli bomb, and both sides will believe their truth. And that’s it. In the old days, you used to be able to find out what actually happened. Now people just go ‘No, that’s our truth, and you’re lying’. And it’s terrifying. And then with AI approaching as well, where you’re gonna deep-fake people…”

It’s the extremes of ideology he finds the most terrifying. “I mistrust anyone who thinks they’re right,” Joly adds. “I’m not right. I don’t know a thing. And today the worst thing a politician can do is change their mind and be a ‘flip-flopper’. But that’s the politician I want. I want someone who can admit, ‘I think I’m wrong, and I’ve changed my mind’. It shows you’re thinking.

“My ambition was to meet a flat-Earther. I wanted to sit across the table and ask, ‘You genuinely believe the Earth is flat?’ which I did twice. They weren’t what I expected. You tend to think they’re all thick but they’re not. If anything, they’re quite smart.”

Another thing Joly, 56, who found fame with hidden camera show Trigger Happy TV in the early noughties, quickly discovered was that no matter how crackers something might sound, there’s always someone, somewhere who’ll take it seriously.

Indeed, many conspiracy theories started life as online jokes.There’s even a name for this phenomenon: Poe’s Law, an internet-era adage claiming it’s impossible to parody extreme views because a minority will take the send-up at face value.

Or, to put it more simply, as Joly tells me: “You can’t outcrazy crazy.”

• The Conspiracy Tourist by Dom Joly (Little, Brown, £22) is out now. Visit expressbookshop.com or call Express Bookshop on 020 3176 3832. Free UK P&P on orders over £25. Tickets for Dom Joly: The Conspiracy Tour stage shows in February and March 2024 are available via domjoly.tv