If you spent the middle-range of childhood during a particular decade (the 1980s), having been born into a particular kind of family (old Labour broadly covers it, but mung beans were probably involved), you will be inclined to find a conspiracy theory wherever a conspiracy theory could conceivably be found.
This is either (a) because there really were a lot of conspiracies in the 1980s (b) because the 1980s were a more political decade than, say, the 1990s, and wherever there is grassroots opposition to a government, it is assumed by the grassroots that the government is trying to kill, or at least bug, them, or (c) because there were some good conspiracy films made at that time, most of them featuring Gabriel Byrne. We won't know the answer for 75 years after any given event, which is the period deemed by the Public Records Office to be "well, we may as well tell them now, surely they can't still mind?" time.
Since then it's been passé to have a conspiracy theory of any kind. The phrase "that's just a conspiracy theory" has become a kind of insult, capable of discrediting its proponent immediately, as if the idea of anything sinister happening anywhere at all were so outlandish that just by dint of questioning what you were told, you might as well have said: "I believe in UFOs and send my cat postcards when I'm on holiday."
Furthermore, since conspiracies are so silly, nobody ever comes out with them after a prominent death - the aftermath of a tragedy is, by consensus, the last time anyone should be thinking silly things, even though (paradoxically) most decent conspiracies do have a death or two involved somewhere. Consequently, only one person voiced any suspicion after the death of David Kelly, and that was Darcus Howe, reporting in the New Statesman the conversation that occurred down his local (it wasn't suicide, the CIA did it; or MI5, difficult to say). Even while you've got to be impressed at his neck-sticking-out, at the back of your 1990s-trained mind, you're thinking: "That's just a conspiracy theory!"
But this week things are all starting to look a bit Hollywood. Which is to say that, if you were going to write a film about a real conspiracy, and you didn't want to make it too complicated, this is what you'd write. Scene 56 sees the Labour MP Eric Illsley casting doubt on the mental state of Andrew Gilligan, calling him "close to the edge". With respect to the floppiness of the expression, it basically means he's suicidal. And when people who already don't like you start questioning your will to live, be honest, doesn't a loud, Hitchcockian "ching ching ching" go off in your head?