Luckily for Derren Brown, this leaves a power vacuum. Brown, a small, slight lad from Bristol with an affectedly Mephistophelean beard, is now, officially, the coolest magic act on television. So cool that he isn’t even strictly a magic act, but a new hybrid of his own invention. Brown is a “psychological illusionist”. He messes with people’s minds. His tricks include getting a dog track to pay out on a losing ticket simply by insisting that it was, in fact, a winner; beating a chess grandmaster at Mastermind in a single move by predicting every one of his coloured peg choices; and “touching” blindfolded people from across the room with a simple gesture.

Amazing as these tricks are, they pale into insignificance before Sunday night’s offering. For Derren is preparing to put not just his money where his mouth is, but his own life — testing his lie-detecting skills to the max in a deadly game of Russian Roulette. Here’s the official drill: “A member of the public will load a real handgun with one bullet and then hand it to Derren. He will then use his ability to read people to determine which chamber contains the bullet, by putting the gun to his head and pulling the trigger until he comes to the live chamber.”

He has tried to stack the odds in his favour: 12,000 Channel 4 viewers applied to shoot the gun; 1,500 were invited to send in a video; of the 500 who did, 100 were invited to London. These have now been whittled down to five, of whom this weekend only one, hand-picked by Brown as being easiest to “read”, will load the bullet into the chamber. All the same, if it’s for real, then he is very confident indeed of his ability to read people. If it’s not, then it is a travesty and unworthy of Channel 4. Either way, many viewers will remain cynical.

“I realise that,” says Brown, over a hearty condemned man’s last meal in Hampstead, where he currently lives in a squat, “and it’s partly down to the programme to show you: it is a real gun and it is a real bullet.” Then are you scared? “No. And yes.” So there will come a moment when you hold a real gun to your head? “Yes.” And pull the trigger? “Yes.” And if you get it wrong, that bullet will blow your brains out? “Definitely, if I get it wrong; there’s no way of skimping on that at all.” No special device in the gun? No failsafe? No producer interrupting at the last minute? “No, you cannot do that. Anyway it’s live, so that would be difficult. Even if we switched the bullet for a blank, at that distance it would still kill me. So it is what it is.”

If any pinches of salt are still being taken by readers, Brown has only himself to blame. Here’s what he says next: “I hope part of the appeal of the show, and of the series generally, is in trying to work out how it’s done, and where the line is between honest psychological technique and magic technique; where one ends and the other starts.”

To illustrate, he cites his own favourite stunt, and that of many viewers, when he called in two advertising executives to develop a campaign for a taxidermist. The poster that the two arrived at after an hour of brainstorming was almost exactly the same as the one Brown had left in a sealed envelope before they began. How on earth? With flashbacks, Brown proceeds to show the viewer exactly how: by littering the ad execs’ journey to his office with subliminal messages — fragments of the slogan and image printed on T-shirts, posters, shop windows — that they never consciously saw.

It’s those expeditions into the subconscious that are Brown’s true fascination. He is a fine close-up magician, too, but that’s not his trademark. It’s beating people incessantly at “stone-paper-scissors”, guessing names or favourite chat-up lines by looking deep into women’s eyes, making everyone in a shopping mall raise their hand simultaneously by delivering hidden prompts over the tannoy.

And how does he get bookmakers to pay out on losing tickets? Is it a kind of hypnotism, or is it misdirection — slipping them a new note while slapping the other hand on the counter? “There are patterns of behaviour that people fall into. If someone says something totally unexpected you kind of zone out. It’s a good way of dealing with someone aggressive on the street, to say something totally out of context; it confuses them. And in that moment they become very suggestible, so if you give them an instruction it’s a relief from the confusion. It’s a very common technique — politicians use it, they dazzle you with statistics and then sum up at the end with what they want you to accept. The girls at the Tote are doing these repeated patterns all day long, and it’s about interrupting it, confusing them.”

Often he will establish a quick rapport with a “cold reading” — lulling a new subject into a state of suggestibility by telling them things that they believe are specific to themselves. For instance, David Blaine, in his book Mysterious Stranger, includes a “cold reading” passage addressed directly to the reader. It mixes such universal platitudes as “you are a very sensitive type of person. . . sometimes you are overly analytical, but it’s better to try to live spontaneously” with the chillingly specific: “You have a scar on your left knee.” Apparently, most people do — mine from running through a window.

“Yes, that’s devastating if you don’t know how it works,” agrees Brown. “Or the scar’s on your other knee, which seems close enough; or people ask their parents and discover that they did hurt their knee when very young so they think wow, he knew that about me when even I didn’t!”

What’s most unusual about Brown is that he tells his subjects — and the viewer — exactly how he’s reading them, how he’s planting thoughts in their heads. Knowing it makes them no less susceptible. Possibly the reverse. Strangely for a man who delights in mystifying his audience, and who describes himself as having been a “very happy-clappy Christian” when younger, he abhors mumbo-jumbo.

“Part of the unspoken philosophy behind the show is shaking up any kind of true believers. It’s nice to bother the psychics by saying it’s not psychic, and nice to bother the scientists who can’t quite explain it either.”

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