Only the Lib-Dems can beat the Tories
In an ICM poll for the Sunday Telegraph Labour have fallen to third place. The proportions are Conservative 40%, Labour 22%, Lib-Dem 25%. This could be a rogue, simply the result of random sampling error. It could be a blip, a short term reaction to the expenses scandal. Or it could be that the Lib-Dems have crossed the tipping point.
Under First Past the Post voting there is only space for two parties. Voters tend to be attracted to only one of two parties because even if the party that they vote for does not truly reflect their views it will keep the other lot out. That the Liberals have survived at all (which at times looked doubtful) was probably because they occupied the extremely important strategic ground at the middle of the political spectrum.
While under a uniform national swing this result would mean that the Lib-Dems are still the third party there is a chance that they could becoming the party to keep the other lot out for enough people, with the other lot being both Labour and the Conservatives, that they jump far above what a uniform swing predicts as people try to keep both the other main parties out. If that happens, if the Lib-Dems become the party to keep the other lot out, then suddenly the dynamics of the political environment change. This chaotic environment gets tipped out the equilibrium where people voted Labour to keep the Conservatives out and Conservative to keep Labour out, with the Lib-Dems ignored, to a new equilibrium where people vote Lib-Dem to keep the Conservatives out and vote Conservative to keep the Lib-Dems out. Kind of like how the Lorenz Attractor becomes a Repulsor when the variables are set over a certain threshold.
Labour would be reduced to a rump or hard core true believers on the left, and unlike the Lib-Dems, this would pull them further and further away from the vital centre ground so making them less and less likely to ever be a significant electoral force again. Or this poll might be a rogue.