Your argument for AV, or to give it's real name, Proportional Representation, so that the actual votes by the public all count towards a single total to get a party into power won't achieve this because the votes are still isolated into each constituency, so the best anyone under an AV system could hope for is that in more marginal seats when the results are not clear cut and the percentage lead doesn't give a clear majority, the redistributed votes might tip the balance and get the second party into power for that seat.

I understand those in support of AV's point of view, especially when a seat might be held by just 100 votes, but I personally want to know that the single vote I make carries weight behind the single party I'm voting for, not that it could end up supporting someone I don't want in power.