A better explanation
Chris Brooke makes the rather good (though presumably checkable if I could read Spanish and their polls are like ours) suggestion that the victory for the socialists in Spain yesterday was due to the higher turnout, itself a function of the demonstrations and greater political awareness after the bombing.Certainly this is what would happen in the UK if the turnout increased. Most opinion polls that show the parties level-pegging are based on a 50% turnout; they would show Labour about 5% in the lead on a 75% turnout. That's about the magnitudes we saw in Spain.
A great day for democracy, as Chris says.
Update: Doing a regression on ICM's latest poll, it seems that for every 1% increase in turnout, Labour's lead rises by 0.2%. I've got a lovely chart but unfortunately I can't find my ftp details.