I’m going to overstate this to make a point which isn't new, but is worth rehashing I think.
The modern electorate votes against its perceived enemies rather than voting for a party it supports. A political enemy is anyone who threatens to disturb a voter’s comfort zone, so Labour voters are on the whole voting against the Tories, not for Labour and vice versa.
Lib Dems are political snobs – they are voting against both Labour and Tory because they see both as beyond the pale - which of course they are. Lib Dem voters aren’t voting for toads like Nick Clegg though, because who would?
This probably applies to the tiny sprinkling of party activists too, as well as a much larger number of voters who are not party members and I think it has always been the case. Voters have little or no interest in the party they habitually vote for, which is one reason party membership is so low.
We slot people into many social groups with many subtle and not so subtle nuances to control the slotting. Friends, family, colleagues, fellow nationals, fellow language or dialect speakers, fellow members of a social class, profession or club and so on and so on. One of these groups is enemy.
We can apply enemy to many people with numerous graded distinctions, but at a political level, we do not really have an opposite of enemy. We do not recognize political friends for example.
The only real alternative to a political enemy is a leader, but people we class as leader at a national level have to possess certain characteristics such as gravitas, political wisdom and a certain degree of mystique. These characteristics are not commonly encountered, particularly in the modern world where mystique has largely been abolished. Mystique helped where gravitas and political wisdom were in short supply.
So, for example, nobody actually expects Ed Miliband to make a successful Prime Minister unless he is very lucky with the ebb and flow of events he cannot control. Yet if nothing else comes into play, he may well win the next election simply because David Cameron and Nick Clegg have attracted the label enemy by not attending to our comforts.
I'm sure they are all aware of it too, which is why modern politics is so dire. They know we only ever vote against them, never for them. So nothing positive or worthwhile ever gets done, just endless dodgy deals with pressure groups while bureaucrats have a field day.
It's the effect of our dimwitted voting patterns of course, our collective failure to see that all three main UK political parties are the political enemy, but I suspect it’s too late now. Change, if it comes, will be imposed from beyond our shores.