Since Par Avion episode we now know that John went in to the basement part and took some C4 so he lied when he said he didn't know about it, but I still think he didn't know enter 77 would blow the place up.
I agree with everyone that said the C4 was added long after the Flame station was originaly built. And I thought it was odd or noteworthy that there were wires hanging down from the ceiling to the chess computer. these wires looked like the same wires running to the C4.

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Doctor playing golf. Woo, boy howdy, now I've heard everything. What's next, cop eating a donut?