Think about it: the son of the Manse, the man with the moral compass, leads by example by resigning and calling for a wholesale clean-up of Parliament. He gets remembered for doing the decent thing as he and then dozens of other MPs quit and Alan Johnson, squeaky clean, gets to take on David Cameron (who himself, of course, has some questions to answer when it comes to expenses).
It's interesting, and I think it plays out to the same sympathy card that the one-eyed freak is going to try and play anyway. Is it a game-changer? I don't think so. Labour are spent and reeling. Johnson, I think, is too canny to want to lead his party to a massive defeat. And really, Cameron would have to be exposed as Madeleine McCann's kidnapper to get the people out of the mindset that it's the Tories' turn to boss us around.
But it would certainly make it interesting.
No, I think the way it's going to play out is Gorgon or some other makeweight is going to lead the party to its doom. (Alan) Johnson will then become Prime Minister Cameron's bete noire.