A similar point is made by Edmund Conway in a comment piece for the Telegraph today:
All of which inspires a question which may seem counter-factual to most CoffeeHousers: is the country better off if Labour doesn't supplant Brown before the next election? So far as our economy is concerned, is it actually more desirable that Brown stays in place for the next few months, so that a Tory majority is more likely? Something to mull over on a Wednesday afternoon...“
"Part of the reason the debt markets have remained relatively sanguine in the face of a staggering collapse in tax revenues and increase in the deficit is that they are assuming a Conservative victory: when the prospect of an Alan Johnson leadership challenge briefly made a hung parliament more likely, they panicked."