UKIP polled 3% of the national vote in 2010, and yet their stock has risen to nearer 6% in latest opinion polls; a rise fueled in no small part because of the Tory party becoming a little more moderate in coalition and certainly because of their cooperative stance on the EU.
My calculations are far too rough and laden with assumptions to publish fully, but taking the notional results based on the 2010 elections under the proposed new boundaries for Scotland and England (assuming equal changes for each party in Wales, as their review isn't out yet to my knowledge), and attributing a rise to the UKIP vote of 3% universally at the expense of the Tories in it's entirety will mean the difference in 2015 between another Tory/Lib Dem coalition, and a Labour/Lib Dem coalition (or minority governments of either of the leading parties aforementioned).
In simple terms, the rise in UKIP support does nothing but split the vote of the "right" of the political spectrum, i.e. the Tories. Given also that we know that the Tories are suffering in marginals where the Lib Dem vote is holding it's own (most likely due to tactical voting by Labour supporters that still understand ends justify the means in a FPTP system). The effect of this is that such a rise of the UKIP party's vote shifts about 20 seats to Labour as it loses it's marginal Labour/Tory fights even more easily than the current rise in Labour support would suggest.
The future is less than certain and all kinds of changes could happen in what is a very volatile political landscape over the next 3 years, so none of this is a given. UKIP support could fall back as the Tories find a way to placate the far right, or it could rise higher as disenfranchisement grows. Lib Dem's stock could be anywhere in 2015 and the battle between Labour and the Tories is far from over with the cuts and growth outcomes uncertain.
One thing is very probable though: When taking in to account UKIP's numbers, if those people were to put the Tories as their second preference under an AV election, the Tories would have a narrow but absolute majority of their own, even if Labour was as popular at the next election as they are currently in the polls.
I think that the Conservative party will come to rue standing against the idea of an AV system in the end, and perhaps AV supporters like myself will end up having the last laugh after all.