It’s virtually impossible to find any sort of meaty arguments for or against replacing FPTP with the AV system, principally, I now suspect, because being a compromise system that nobody really wants, there aren’t any.
I’m opposed to pure proportional representation because it produces corrupt, irremovable coalition governments and severs the already often weak link between the MP and his local constituents. But AV isn’t a proportional system, merely a more complex version of FPTP which might or might not be marginally better than the simple system we have at the moment. Some argue that the simplicity of our current system is itself a virtue, others complain about the ‘wasted’ votes in very safe seats (which as a complaint has some legitimacy, but there is a difference between having your preferred candidate lose and ‘wasting’ your vote, and anyway it’s still a lesser problem than those produced by proportional representation).
There’s no real reason why the usual progressive London suspects (Fry, Izzard etc) should be particularly keen on AV, other than that they just like making constitutional changes. And there’s no real reason for conservatives to vehemently oppose AV, other than that they dislike making constitutional changes.
On balance I think AV is probably a slightly better system than the current one; but if it’s supposed to be, as Lib Dems hope, a ‘step towards proper PR’ then I have a stronger reason to oppose it. The conclusion being, I don’t really care much either way, and will probably decide at the very last minute. Which apathetic attitude captures the general mood, I suspect.