According to the Times, Boris Johnson won't be standing down as MP for Henley if he wins the London Mayor contest today. This can only be because the Tories think that they might get beaten in any by-election.
This is David Cameron's new emboldened Conservative Party that is confidently predicting more than 200 seat gains and over 40% of the poll. And they're scared. Of the little old Liberal Democrats.
(Oh, yes. And announcing a massive backtrack on polling day when the broadcasters won't run any 'contest' stories is a very, very cheap trick)