I believe Purnell when he says he acted alone - if he waited for some co-ordinated attempt he would be waiting forever. Even those close to Purnell had no inkling that he was preparing to do this - the secret was so well-kept that even No.10 didn't know until 9.50pm.
Of course, if Purnell was offered education, that means Ed Balls has porbably been offered the Chancellorship. My hunch is that this was likely to be the trigger for Purnell and, if such a move is confirmed, it could be a trigger for many other ministers. There is something about Balls as Chancellor that is simply incendiary: it would be the ultimate sign of a bunker government. Reduced to Brown, his aides and a few has-beens.
Brown got rid of Blair by getting private secretaries to resign hour after hour. It seems Brown is going to go after Cabinet ministers resign day after day.
UPDATE AT 12.15AM: And now Brown's attack dogs come out. Peter Kilfoyle, who is one of the half dozen remaining Brown loyalists, has just been on Sky News saying that the Cabinet members who have resigned "are fixed on their own careers" (how can he say that of people resigning?), and Purnell "has never had a proper job" (unlike, say, Ed Balls and pre-1983 Gordon Brown) and "shouldn't be in the Cabinet," and "has no political acumen whatsoever". Adam Boulton replied: "If you think he's such an idiot, what does that say about the man who promoted him?"
The counter-attack is that this is a "Blairite coup," as Diane Abbott claimed. Except, Diane, the point of a coup is to take control. And is Tommy Watson a Blairite? Why is John Hutton going against Purnell? Brown's line - this is an attempt at a Blairite restoration - won't wash.
UPDATE AT 12.30AM: No10 has denied that Purnell was offered education. I haven't seen what technical weasel words they have used, but they are fibbing. I am 100% confident. And I suspect this won't be the last set of fibs that No10 tell if the reshuffle keeps falling apart at this rate.