A significant change has occurred since the Budget. From the undeclared granny tax, to the silliness over pasties, to the unnecessary panic over petrol, no single one of the Government's stumbles was momentous in itself. Taken together, however, they have for the first time raised questions as to the competence rather than the politics of the Conservative leadership.

The judgement of the polls is unequivocal: a three percentage point drop in support for the Tories. At another time, such details might be of only incidental interest. After all, a Budget delivered in hard times was never likely to win a chorus of approval, and after two years most governments are starting to lose their gloss.

What is striking, though, is that Liberal Democrat support has not so much as twitched in response, and Labour has picked up but a single point. With local elections and the London mayoral race looming, all the main parties have much to worry about.

Mr Miliband cannot fail to make headway on 3 May, given that the last round of local votes were held when Gordon Brown was leading a deeply unpopular Labour Government. But there are two major urban battlegrounds where the outcomes are by no means certain and the stakes are high indeed.

In the aftermath of the Budget, it is David Cameron and George Osborne who are struggling to regain their poise. If Boris Johnson loses the London mayoral race, the newly-nagging sense of drift will be hard to shift. But if Labour either fails to beat Mr Johnson, or loses Glasgow City Council, or both, then questions over Mr Miliband's leadership will prove a more than effective distraction.

These are unusual political times. An increasingly disillusioned electorate is turning away from the main parties, clearing the way for those at the margins. Labour has already had one shock, with George Galloway's spectacular win in Bradford West. The threat from the SNP in the long-held fiefdom of Glasgow is more troubling still. For the Tories, the danger comes from Ukip. Whatever happens on 3 May, more will be won and lost than 5,000 council seats and one mayoralty.