FOR now, the conventional wisdom remains that Scottish Labour’s tribulations do not reflect on Jim Murphy to any great extent, or on his alleged star quality. But if the pattern currently shown by the polls persists for much longer,it will surely have to be acknowledged that, while Murphy may be a very different leader from Johann Lamont, he is no more effective a vote-winner than she was. The new full-scale Scottish poll from ICM suggests that Labour have cut the SNP’s enormous lead by just one per cent over the last three months, which is a trivial change that can most likely be explained by the standard three per cent margin of error.

Unfortunately, ICM didn’t conduct any Scottish polls in the period between the referendum and Labour’s leadership change, so it’s not possible to use this poll to directly measure any “Murphy effect”. However, the static position is entirely consistent with what we’ve seen from other pollsters that were active when Lamont was still in harness. Although it’s not entirely clear when the SNP surge occurred, there is now overwhelming evidence that a mammoth gap between the SNP and Labour has survived wholly intact since the latter half of October.

While Labour as a party are merely stuck in a deep hole, there are signs that Murphy himself is still sinking. ICM has corroborated the recent YouGov finding that his personal rating has dropped significantly since his earliest days as leader. While he was never popular with many supporters of independence, it appears the bulk of voters were initially prepared to give him a chance. Clearly they haven’t been bowled over by what they’ve seen since then, and as a result Nicola Sturgeon’s net approval rating is now 23 points better than Murphy’s, compared to a 13-point gap in December.

It’s important to stress that although the various polling firms are in broad agreement about the trend, they differ sharply on the question of just how enormous the SNP lead is, and in some cases those differences fall well outside the claimed margin of error. In other words, we already know not all of the firms are getting it right.

Exactly the same was true during the referendum campaign, but oddly there is no correlation between which firms produced better results for the Yes camp and which are now producing the best results for the SNP. ICM was generally on the “Yes-friendly” end of the spectrum, but its SNP lead of 16-17% is lower than the average from most other firms.

Part of the explanation for this is likely to be its use of the so-called “spiral of silence” adjustment devised after the polling disaster of 1992, when all firms failed to detect the strength of the Conservatives. It’s a final adjustment that takes place after all other weightings have been applied, and it reassigns a portion of undecided voters to the party they voted for in the last General Election.

Election results since 1992 have seemingly confirmed the wisdom of this approach, but it has yet to be put to the test in the extraordinary circumstances we now find ourselves in. The problem is not merely that the shift in opinion is so unprecedented in scale, but also that some of the undecided voters being reassigned to Labour by ICM will already have voted SNP since 2010, most importantly in the Holyrood landslide of 2011. Can such people really be considered “default Labour” voters any more?

The possibility that ICM is closest to the mark means that Labour can at least cling to the hope that a late fightback might save their bacon in a respectable number of seats. But if it turns out that Ipsos MORI’s mind-boggling SNP leads in the high 20s are more accurate, the point of no return may already have been long since passed.

James Kelly is the Scot Goes Pop blogger