Gordon Brown and the Labour Party woke this morning to the mother of all political hangovers, and the dread knowledge that the situation might seem very much worse before the day is out, writes Frank Millar, London Editor.
For as David Cameron celebrated an estimated 20 point lead and some 44 per cent of the popular vote, advances in the north as well as the south of England, and the collapse of once impregnable Labour citadels in Wales, the Conservative leader and his colleagues were finally allowing themselves to believe that Boris Johnson might just put the icing on the cake with a spectacular victory over Ken Livingstone in London.
It is always possible to make too much of "mid-term" elections. And they emphatically do not inform us about what will happen in the general election Gordon Brown need not call (technically at least) another two years. That said, a lot seems to have changed in the space of just two days.
On Thursday it was entirely reasonable to posit that a third-term victory for the incumbent Mayor Livingstone would offer at least some respite for the embattled prime minister.
By midday today it seemed unlikely that even a win for Ken would do anything to mask the best night for the Tories since John Major's surprise general election victory in 1992 - or Labour's worst local election performance in forty years.
It is now clear, moreover, that a defeat for Livingstone would make Brown's position instantly worse. For as the LSE's London government expert Tony Travers told the BBC earlier: "Remember, Ken was always worth more votes than the Labour Party."
The promised relief for Brown was that Livingstone was thought unlikely to blame Labour's national difficulties should he lose control of City Hall. But as Travers observes, if Ken loses to Boris "it will be seen as a symptom of a much deeper problem."
In simple terms, if even the original "Mr London" can't hang on in these circumstances the panic levels among already nervous Labour backbenchers with smallish majorities will likely reach new heights.
Not that they are thinking of a putsch, if only because there is no credible alternative leader to be found. And there really is something rather pathetic in the spectacle of former senior Blairites questioning Brown's authority and criticising his performance when none of them had the courage to stand against him when the opportunity presented itself less than a year ago.
However, it is sobering to reflect that it was less than six months ago that the "new" Labour leader was contemplating a snap general election in which his aides predicted he would destroy Cameron's leadership and put the Conservatives out of office for another generation.
As he hailed "a very big moment" for the Conservative Party this morning, Cameron sounded suitably cautious about the job still to be done. But amid the pop of champagne corks, the Tory leader had the assurance of respected analyst Professor John Curtice that a move to Number 10 in one general election heave is no longer inconceivable.