Schrödinger's Ballot Box

In normal circumstances, today would be no different to any other with its mixture of joy, miracles and pleasantries and tragedies, anger and mourning.  Except we are in the course of a General Election campaign, ten days out from polling day and this is the point that the Labour vote nosedives.  This has happened for three decades now and has oft been explained by 'undecided' or wavering part of the electorate plumping for economic competence, traditionally believed to be the preserve of the Conservative Party.  Even in the heady days of 1997, the support for Labour collapsed by about ten percentage points, to ensure that Tony Blair bagged (or indeed blagged) fewer votes than John Major in 1992, though partially this was due to Labour supporters tactically voting for Liberal Democrat candidates to oust (or suppress) Conservatives.
Ironically, tactical voting may increase the Labour turnout as Unionists in Scotland try and keep out SNP candidates from winning seats.  Yet in England and Wales, the fear that Labour may be in hock to determined Scottish National Party zealots (though Ed Miliband could call the SNP's bluff and dare them to vote down a Labour government) has had its effect.  My mum is wavering in her vote because of fear of damaging the Union if she votes Labour and a Labour-SNP informal alliance is a hot-button issue in all the marginals Labour hopes to win.  Partly to scotch such talk south of the border and to say to former Labour supporters north of the border that a vote for the SNP isn't a surrogate protest vote for the Labour Party, Ed Miliband has ruled out even a 'confidence-and-supply' arrangement with the SNP.  Of course, by enough people not voting Labour because of the 'threat' of a Labour-SNP deal, it could become a self-fulfilling prophecy: Labour becoming the largest party but falling short of an overall majority so far as to not be able even to team up with the Lib Dems (who will lose around half their seats).  It's the electoral equivalent for floating voters of Schrödinger's Cat.