The spotlight now falls on Gordon Brown. What will he do with his Chancellor, especially if it's the case that rules have been broken? In an odd way, the situation is probably helpful and unhelpful for the Dear Leader. Helpful, in that it could pave the way for Darling to be moved from the Treasury and replaced by Ed Balls; meeting - in the most perverse possible fashion - Lib Dem calls for the current Chancellor to get the heave-ho. Unhelpful, in that a dying government could well do without its Chancellor getting caught up in controversy; and that ditching him could set a dangerous precedent over what to do with all those other ministers who have enviable, taxpayer-funded property portfolios.
Overall, though, you have to say that this is almost as damaging for the government as it is for Darling himself. And the idea of Balls stepping into the breach is hardly going to stem Brown's slide towards political oblivion.
So far, Brown seems to be standing by his man in No.11. In an interview on Today this morning, he said that Darling has been a "very good Chancellor, and a very good friend"; adding that: "I don't think there's substance in these allegations." But will he be singing a similar tune after this week's elections? We shall see.