OK, you'll need to read Part One first.
My main thesis is that voting reform is not a strong argument. I know at the minute the nastiness of the electoral system is a central part of the campaign.
First past the post locks people in, it means you can't vote for a party with a small base support for fear of letting in the main opposition. Put anotehr way, First Past teh post works best [sic] when you are faced with only two choices, as soon as a third choice enters it merely becoms a secondary factor working on the choice between the two leading candidates.
Hence famously(ish) Respect helped the Tories win a council election by taking votes off labour (to be precise, more votes than the difference between Labour and Tory). Likewise the referendum party helped remove Major's government by splitting away Tory votes.
Now, most Proportional Systems are set up to reward votes gained only. That is, voting for one party does not objectively become a vote for another. They are also more volatile systems because of this, because parties are seen of having more chance of winning - i.e. that our votes can be effective. Not much point voting Green, say, since they won't win under First Past the Post.
This is a major reason why turnout is dire in areas with thumping Labour majorities. There is just no point voting against them. (Although if you think it's bad here, look at the results from local Elections in Washington DC. The point is, though, that in elections that only return one representative per geographic area, the system is enforcing homogeneity, compelling coalition building. But when that sort of homogeneity doesn't exist in the electorate, that can only happen by covering over the cracks.
Further, given the resources required for an election campaign, and the level of media access required, tehre is a huge incumbancy advantage. The whole concept of 'Main parties' gives them an air of establishment an permenance, backed up by the fact that the warring bands who really make them up are compelled to mask themselves behind the party brand. And of course, whoever controls the party machinery has a further edge in ensuring they can get teh best of the system.
Next post is about how PR challenges this.