“Excuse me, people!” he says. “This is morally and ethically wrong! So let me make a political statement, boys and girls.”

He dramatically pulls off his jumper, to reveal a T-shirt: ‘DOP’ with a red line through it.

“No more!” he shouts above the whoops and applause. “No more!”

Out in the car park, Smith tells me that he has been a sufferer since 2004. “I put a sweatshirt I’d been wearing in the garden over my arm and there was this intense burning, sticking sensation. I thought it was cactus spines. I began picking to get them out, but it wasn’t long before it was all over my body.” He describes “almost an obsession. You just can’t stop picking. You feel the sensation of something that’s trying to come out of your skin. You’ve just got to get in there. And there’s this sense of incredible release when you get something out of it.”

“What are they?” I ask.

“Little particles and things,” he says, his eyes shining. “You feel the sensation of something that’s trying to come out of your skin.” He is pacing back and forth now. He is becoming breathless. “You feel that. And when you try to start picking, sometimes it’s a little fiber, sometimes it’s a little hard lump, sometimes little black specks or pearl-like objects that are round and maybe half a millimeter across. When it comes out, you feel instant relief. It’s something in all my experience that I had never heard of. It made no sense. But I saw it over and over again.”

Sometimes, these fibers can behave in ways that Smith describes as “bizarre.” He tells me of one occasion in which he felt a sharp pain in his eye. “I took off my glasses and looked in the mirror,” he says. “And there was a fiber there. It was white and really, really tiny. I was trying to get it out with my finger, and all of a sudden it moved across the surface of my eye and tried to dig in. I got tweezers and started to pick the thing out of eyeball. I was in terrible pain.”

I am horrified.

“Did it bleed?”

“I’ve still got the scar,” he nods. “When I went to the emergency room and told the story of what had been going on — they called a psychiatrist in! I was like, “Wait a minute, what the heck is going on here?” Fortunately, he didn’t commit me and after another consultation with him he became convinced I was not crazy.”

“So, it was a Morgellons fiber?” I say. “And it moved?”

‘Of course it was a fiber!’ he says. ‘It honest-to-God moved.’

Smith tells me that a Morgellons patient who finds unusual fibers in their skin will typically bring a sample to show their doctor. But when they do this, they’re unknowingly falling into a terrible trap. It is a behavior that is known among medical professionals as ‘the matchbox sign’ and it is used as evidence against them, to prove that they are mentally ill.

“The matchbox sign was first described in about 1930,” he says. “They say it’s an indicator that you have DOP. This is something that infuriates me. It has absolutely zero relevance to anything.”

Back in the UK, of course, Paul received his diagnosis of DOP after taking fiber-smeared cotton to his dermatologist. I tell Greg Smith that, were I to find unexplained particles in my skin, I would probably do exactly the same.

“Of course!” he says. “It’s what anyone would do if they had any sense at all. But the dermatologist will stand ten feet away and diagnose you as delusional.”

“But surely they can see the fibers?”

“They can if they look. But they will not look!”

“And if you try to show them the fibers, that makes you delusional?”

“You’re crazy! You brought this in for them to look at? First step — bang.”

“But this is madness!” I say.

“It’s total madness! It’s inexcusable. Unconscionable.”

We speak about the CDC study. Like almost everyone here, Smith is suspicious of it. There is a widespread acceptance at this conference that the American authorities have already decided that Morgellons is psychological and — in classic hominin style — are merely looking for evidence to reinforce their hunch. Both Smith and Randy Wymore, the molecular biologist who arranged the forensic examination in Tulsa, have repeatedly offered to assist in finding patients, and have been ignored.

“Have you heard of the phrase “Garbage In Garbage Out”?” he says. “It doesn’t matter what conclusion that study comes to, even if it is totally favorable to the Morgellons community. It’s not well designed. It’s trash.”

As he speaks I notice Smith’s exposed skin shows a waxy galaxy of scars. Although he still itches, all of his lesions appear to have healed. It is a remarkable thing. Skeptics believe that Morgellons sores are not made by burrowing parasites but by obsessive scratchers eroding the skin away. If Smith is correct, though, and the creatures are responsible for the sores, how has he managed to stop those creatures creating them?

“I absolutely positively stopped picking,” he tells me.

“And that was it?”

“Sure,” he replies, shrugging somewhat bemusedly, as if what he has just said doesn’t run counter to everything that he is supposed to believe.

That evening, the Morgellons sufferers are enjoying a celebratory enchilada buffet at a suburban Mexican restaurant. Over the lukewarm feast, I have a long conversation with a British conventioneer — a midwife from Ramsgate named Margot.

Earlier in the day, when I first met Margot, she said something that has been loitering in my mind ever since, wanting my attention but not quite sure why or what it is doing there. We were at a cafe, waiting for the man to pass us our change and our lunch. He dropped the coins into our hands and turned to wrap our sandwiches. As he did so, Margot sighed theatrically and gave me a look as if to say, ‘Unbelievable! Did you see that?!’

I had no idea what she meant.

She rolled her eyes and explained, “He touches the money, then he touches our food…”

Tonight, Margot describes a scene which ends up proving no less memorable: her, sat naked in a bath full of bleach, behind a locked door, wearing times-three magnification spectacles, holding a magnifying glass and a nit comb, scraping her face onto sticky office labels and examining the ‘black specks’ that were falling out. Perhaps sensing my reaction, she tries to reassure me: “I was just being analytical,” she insists.

When bathing in bleach all night didn’t help, Margot brought her dermatologist samples of her sticky labels. Shaking his head, he told her, “I can’t tell you how many people bring me specimens of lint and black specks in matchboxes.” She was diagnosed with DOP. Her employment was terminated. “I’m a midwife,” she says, in her defense. “I take urine and blood samples — specimens. So I was taking them a specimen. And that’s what wrecked my life and career.”

As I am talking with Margot, I notice Randy Wymore, the molecular biologist I have been desperate to speak with, sitting at a nearby table. He is a slim, neat man wearing a charcoal shirt, orange tie and tidily squared goatee. When I sit with him, I find him to be incorrigibly bright, light and happy, even when delivering wholly discouraging news.

The first two samples that Wymore sent to the laboratory were not from Morgellons patients, but test fibers gathered from a barn and a cotton bud and then some debris from the filter in an air-conditioning unit. When the technicians correctly identified what they were, Wymore felt confident enough to submit the real things. And, so far, he says, ‘We have not yet exactly replicated the exact results of the forensics people in Tulsa.’

Indeed, the laboratory has found Wymore’s various Morgellons fibers to be: nylon; cotton; a blonde human hair; a fungal residue; a rodent hair; and down, likely from geese or ducks.

“That’s disappointing,” I say.

He leans his head to one side and smiles.

“It is for the most part disappointing,” he says. “But there was a bunch of cellulose that didn’t make sense on one. And another was unknown.”

“Really?”

“Well, they said it was a ‘big fungal fiber.’ But they weren’t completely convinced.”

The next day, nursing practitioner Dr Ginger Savely — who claims to have treated over 500 Morgellons patients — leads an informal discussion in the hotel conference room. Around large circular tables they sit: the oozing and the itchy, the dismissed and the angry. “I’ve seen a fiber go into my glasses,” says one. “I’ve seen one burrow into a pad”; “One of my doctors thinks it’s nanotechnology”; “Check your clothing from China for nematodes”; “Never put your suitcase on the floor of a train”; “I was attacked by a swarm of some type of tiny wasps that seemed to inject parts of their bodies under my skin.”

I am writing the words ‘tiny wasps’ into my notepad when a furious woman with a terrifying itch-scar on her jaw says, “I have Erin Brockovich’s lawyer’s number in my purse. Don’t you think I’m not going to use it.”

“But who are you going to sue?” asks a frail elderly lady two tables away.

We all look expectantly at her. There is a moment of tense quiet.

“I don’t know,” she says.

In a far corner, a woman with a round plaster on a dry, dusty, pinkly scrubbed cheek weeps gently.

Ten minutes later, I am alone in the lobby, attempting to focus my thoughts. My task here is straightforward. Has Paul been failed by his medics, or is he crazy? Are these people infested with uncommon parasites or uncommon beliefs? Over at the reception desk, a conventioneer is complaining loudly, hammering her finger on the counter.

“It’s disgusting! Bugs! In. The. Bed. I’ve already been in two rooms. I had to drive to Walmart to buy fresh linen at 5 a.m. There’s this white stuff all over the counter…”

When she has gone, I approach the desk and ask the receptionist if the weekend has seen a surge in complaints about cleanliness.

“Oh yeah.” She nods towards the conference room. “And they’re all coming from those people.” She leans forward and whispers conspiratorially. “I think it’s part of their condition.”

Satisfied, I retire to the lobby to await my allotted chat with Dr Savely.

“So, what do you think,” I ask her, “about these tiny wasps?”

“Hmmm, no,” she says. “But I haven’t totally dismissed the whole genetically modified organisms thing. Something may have gone amuck.”

“Nanotechnology?” I ask. “Some defense experiment gone awry?”

“If something like that went wrong and got out to the public…”

I decide to confess to Dr Savely my conclusion: that these people are, in fact, crazy.

“These people are not crazy,” she insists. “They’re good, solid people who have been dealt a bad lot.”

A woman approaches the vending machine behind the doctor. Between her palm and the top of her walking stick, there is a layer of tissue paper. We sit there as she creaks slowly past us.

“There’s definitely an element of craziness here,” I say.

“But I truly believe it’s understandable,” she says. “For people to say you’re delusional is very anxiety-provoking. Then they get depressed. Who wouldn’t? Hello! The next stage is usually an obsessive-compulsive thing — paying attention to the body in great detail. But, again, I feel this is understandable in the circumstances.”

Not wholly convinced, I slip back into the conference room, where Margot is using her $1,100 WiFi iPad telescope to examine herself. Suddenly, I have an idea.

“Can I have a go?”

Pushing the lens into my palm, I immediately see a fiber. The group falls into a hush. “Did you clean your hand?” asks Margot. She fetches an anti-bacterial wet-wipe. I scrub and try again. I find an even bigger fiber. I wipe for a second time.

And find another one. Margot looks up at me with wet, sorry eyes. “Are you worried?” She puts a kind, comforting hand on my arm. “Oh, don’t be worried, Will. I’m sure you haven’t got it.”