Re: First Past the Post
Labour and the Tories might be against PR for reasons of self-interest, but I think there's a pretty good argument to say that so are the voting public. I admit that some called AV a miserable compromise, but even so - there was no public appetite for it. Hence it went down in the referendum. And PR doesn't appear on any of the top ten (or even top 20) policy priorities, when you ask voters.
Also, as the Lib Dems found out, our voters don't seem particularly patient with the policy compromises that PR forces. In first-past-the-post you get less control of who and what you can vote for, but you get a known manifesto at the end of it. You are also able to vote for the anyone but so-and-so candidate, so it enables you to kick out the people currently in power.
PR doesn't give you that negative (but I'd argue really important) option and also leaves you mostly with a coalition government, so you don't even know what policies you're going to end up with. That also has its advantages of course, but to claim that PR is a panacea for all our voting problems is just silly. It has as many problems as any other system.