As a first step, AV is a baby step in the right direction - which is better than nothing and something all us reformers can agree upon.
The problem is, a referendum on this is just asking a big question about a little answer. It does nothing to address the underlying problems of safe seats and disproportionality.
Would anyone think it fair if UKIP who came second had won no MEPs in the latest election and Labour who came third got plenty of MEPs? Because that is what would have happened under first-past-the-post. UKIP would have got 100 MPs and the Greens 60 under PR, but zero under FPTP and zero under AV.
Yes any party that can get a million votes will get MPs and MEPs under PR, including the BNP. But isn't the problem that the BNP can get a million votes, not that they get a few MPs or MEPs. The price for gerrymandering the BNP under the carpet is to also deny democracy to many millions of other voters. That is clearly unacceptable.
If we can't agree on PR, lets at least agree on the need for a referendum on whether we should have a proper proportional system. If people reject PR in a referendum then maybe we reformers will shut up. But if you never let the people decide, we most certainly will not shut up.