It’s hard for an Irish voter to comprehend the stupidity of the British voting system. Your vote only matters if you vote for the “right” candidate in the “right” constituency. Huh? But there you have it, with British Anti-PR people saying that the only electoral system that will work in Britain is the one so crude as to be the electoral equivalent of signing one’s name with an ‘X’ using a crayon.
The rise in the Lib Dem vote, apparently at the cost of Labour votes, will help the Tories if individual Lib Dem and Labour voters aren’t smart in how they vote in their individual constituencies. You could have the bizarre situation where the Lib Dem vote rises nationally, in seats where the Lib Dems have no chance, thus taking votes from Labour candidates and letting the Tory squeeze through. Likewise, you could see the Lib Dems, who have lost some votes to the Tories, losing seats because Labour voters still vote Labour in seats where Labour is in third place. It all happened in 1983, where Labour and the SDP/Liberal Alliance got 52% of the vote to the Tories 42% (the Tory vote actually fell, something which has been forgotten in Thatcherite history) yet Mrs Thatcher got a 144 seat majority, the biggest majority since the Labour landslide of 1945. of course, this all assumes that Labour and Lib Dem voters are interchangable. They’re not, and no Tory leader has done more than David Cameron to reach out to Lib Dem voters, with considerable success. But the reality is that if you want a liberal voice in British politics, you need electoral reform, and the Tories are the absolute obstacle to that.
Ironically, Labour wouldn’t have this problem if it had legislated for the Alternative Vote, which deals with this exact problem, but then Labour has always shown itself to have a stunning capacity for sabotaging itself.
One final point: There is a particular dilemma for Lib Dem voters, in that such is the strong performance of the party, it may actually suit the party in the long term to boost its share of the vote even if it means Labour losing seats. After all, having Labour come third yet end up with more seats than the Lib Dems would be a stunning indictment of how unfair FPTP is. But this assumes that the Tories are going to win anyway, and the result is more about symbolism than actual power.