I have to assume it's fake (he's an actor). If it's not fake, then the amount of work that would go into it would be ridiculous, and there would be a lot of things that could go wrong and ruin the whole thing. Plus the possible legal troubles. And from the wikipedia page "Brown claimed that to keep Steven safe during Apocalypse and in the aftermath (ensuring he doesn't suffer nightmares or posttraumatic stress disorder), there will be a subtle hint embedded deep in Steven's mind that will stop him ending up in mortal fear of such an event and reassuring him", which sounds like so much BS it's not even funny.
So why go through all that when just having him be an actor would be a million times easier? I'm convinced they wouldn't.
I really enjoy most of Derren Brown's stuff, but these super-elaborate stunts are among his least interesting, in my opinion.
I think the guy was psychologically protected by the fact Brown solicits people for his stunts and they know and have agreed to participate in something, though they know not exactly what. I can't believe in all cases the participants don't soon realize, "Oh, this must be the Derren Brown thing playing out!"
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