What Government will the UK have after the 2015 General Election?
If enough English voters move right and vote UKIP instead of Conservative, it is unlikely that there will be many, if any, UKIP MPs but the Conservatives may lose enough seats to give Labour a majority. So the voters would have moved right but Parliament and the Government would have moved left. And they call it democracy!
But there is now evidence that the SNP may almost wipe out Labour in Scotland, although most SNP candidates would win with minority votes. (The pro-UK vote would be split between Labour, Liberal Democrat and Conservative.) If Labour lost many of its 40 or so seats in Scotland to the SNP (i.e. if Scotland moved left), the centre-right Conservatives could be the largest party in the Commons with first claim to form a Government.
Of course, a coalition of Labour and SNP might be able to deny Government to the Conservatives but what an uneasy coalition that would be if the SNP had reached that position by unseating many Labour MPs! Also, would the SNP govern for the benefit of the UK as a whole, which should be the purpose of the UK Government of any political persuasion, or would it extract as much as it could from Labour to further Scottish independence?
Single Transferable Vote (STV) would reduce these problems.
With STV, English UKIP voters could give their next preferences to Conservative candidates to avoid splitting the right-of-centre vote and letting Labour win on a minority of votes.
With STV, Scottish supporters of the UK could give their next preferences to pro-UK candidates (i.e. Labour, Liberal Democrat or Conservative candidates) to avoid splitting the pro-UK vote.
Overall, the House of Commons would be more representative with STV of voters in every part of the UK and of the UK as a whole.