You said you didn't understand why people would prefer the present scenario. I suggest, admittedly with something that could be interpreted as a snark, that most people do for a very good reason.

I can understand some objections to fair voting systems. Self interest is the biggest one: many Tory and Labour MPs are happy to lose power at some elections in exchange for the chance to win absolute power at other elections. This is David Cameron's real objection, not the 'oh, you might get a BNP MP elected'.

But I do not understand why you prefer a system where your General Election vote is irrelevant and means you have - despite the wishes of a majority of your fellow constituents - an MP who has voted strongly against a transparent Parliament, strongly for introducing ID cards, very strongly for introducing foundation hospitals, strongly for introducing student top-up fees, very strongly for Labour's anti-terrorism laws, very strongly for the Iraq war, very strongly against an investigation into the Iraq war, and very strongly for replacing Trident.

It seems an excessively high price to reduce the chances of the BNP getting an MP.