I'm still unsure of how he did it. I saw the wednesday clip live, and then watched his 'explanation' on Saturday.
I didn't believe a word of the 'pure math' explanation; Automatic writing? Using the Mean Average? My arse.
The 'Insider' explanation held a little more water with me, but still seemed a bit far fetched.
The 'Split Screen' idea that has been doing the rounds on the net seems, at least to me, to be the most plausible. Though a little dissapointing, considering this is Derren Brown we're talking about. Someone I highly admire, for his understanding of human psychology and abilities of manipulation.
Here's the link that explains the 'Split Screen' theory, if you want to read it.
I'll be watching the rest of the series with a critical eye, though the next episode looks to be thoroughly interesting.