YouGov's latest polling on the AV referendum shows the NO campaign opening up a clear lead over YES. Taking into account people's likelihood to vote on the 5th May and excluding those who say don't know, our headline figures are YES 42%, NO 58%. The sixteen point lead is identical to that shown in an ICM poll for the Guardian yesterday.
The reason for the sudden jump in the NO campaign lead appears to be all down to Conservative voters. In the weeks YouGov have been tracking opinion on AV Liberal Democrat voters have been consistently strongly in favour of AV. Labour voters have relatively evenly split in how they will vote, they were slightly more likely to vote YES at the start of March, but in the last few weeks have split almost exactly down the middle.
Contrast this relatively stable picture with what our polls have shown about Tory voters. Conservative supporters have consistently opposed AV, but their opposition has become far firmer and more robust over recent weeks. A month ago they were opposed to AV by 58% to 22%, a week ago their opposition had crept up to 62% to 23%. This week Conservative voters split overwhelmingly (76% to 14%) against AV, presumably as a result of David Cameron throwing the full weight of the Conservative machine behind the NO campaign.
If Conservative voters continue to oppose AV in proportions of around 5-1, and Liberal Democrat supporters continue to support AV in roughly the same proportions, then as a rough rule of thumb Labour voters would have to back AV by more than 2-1 in order for the YES campaign to win. None of our recent polling has shown Labour voters backing AV in anything like these proportions.
With just over two weeks to go until polling day (and with the guarantee that several days of that will be dominated by coverage of the Royal Wedding, rather than the AV referendum) the amount of time for the YES campaign to regain the momentum away from NO is rapidly disappearing.