Labour used to believe it would see political gains under AV, exchanging second preference votes with the liberal democrats, and helping to marshall anti-tory sentiment more generally.Things have changed. Since Nick Clegg made the AV referendum a non-negotiable position in last year's coalition agreement many of the left-leaning lib dems have fled to labour, and many of those who remain would support the tories by way of second preference-- even conservative voters seem closer to the lib dem orange book position.
The case for AV is a positive one, and as the maxim in law goes: He who asserts must prove. It is a change from the status quo, in some ways wounded by being a small change, in other ways represented as a dangerous experiment by opponents; most who might want change are underwhelmed by AV, and most others are easily put off by scare tactics. The No camp does not *need* to make a good argument, they can subsist on relatively frivolous arguments. And contradiction is no obstacle.
They can argue that it would help extremist parties *and* argue it would make parliament less representative, and amplify majorities. They can argue that it's a dangerous change, and that it's a miserable little compromise. And worst of all, of course, they can say things which are simply untrue, because few proponents of AV can masterfully convey the realities in a short space of time and in a commanding and convincing manner.
But the tendency of many in Labour to apply these same tactics has proven especially gut-wrenching. Undeniably, the tories stand to gain with the boundary changes, and labour (http://ukpollingreport.co.uk/blog/archives/3424) certainly may not benefit from AV, and given the sorts of frankly disingenuous arguments put forth by the likes of Flint, this is increasingly a transparently political issue.
There are many positions in politics which make me angry, arguments over economics and other issues which seem fatuous and invidious to me, but which I can at least believe may be genuinely held. I think we all experience that. Witnessing the labour contribution to the AV no campaign however has been an unpleasant and castigating experience for my inner idealist. And it is difficult to see how this can end well.
Ultimately, a great deal will be driven by turnout.