He publicly berated the film’s presenter, Andrew Maxwell: “You weren’t there, man. You just have this obedient psychology.” But the more experts he met, the more troubled Veitch became. Finally, when it was shown to him that the towers didn’t, in fact, collapse in a manner consistent with a controlled explosion, and how preposterous his notion was that teams of secret operatives had somehow planted thousands of high explosives in the buildings, he admitted defeat.

“This is hard, you know, because I’ve hung on to these ideas for years now,” he told Maxwell. “I’ve always hung out with people who say, ‘Yeah, conspiracy! 9/11 demolition!’ But now I’ve spoken to a guy who’s explained it. And it makes sense.”

Back in his hotel room, he phoned his girlfriend. “I don’t think 9/11 was an inside job,” confessed Veitch. For a moment, there was silence. “You’re probably just tired,” she said. But by the third day of filming Veitch was so excited by what he’d learnt he decided to post his thoughts on his YouTube channel. And that was when all hell broke loose.

“It was relentless,” he says. “A guy in Manchester set up a YouTube channel called ‘Kill Charlie Veitch’. It said, ‘Charlie, I hope you know I’m going to come and kill you. Enjoy your last few days. Goodbye.’ So many hate videos were posted – my face superimposed on a pig and someone’s killing the pig.” Another message featured images of his sister’s young children incorporated within a video of child pornography.