Ice-cool ICM poll indicates impressive 16% lead for SNP

This morning has seen the publication of only the second full-scale Scottish poll since the referendum from ICM - regarded by some as the UK's "gold standard" polling organisation.

Scottish voting intentions for the May 2015 UK general election (ICM, 13th -19th March) :

SNP 43% (n/c)
Labour 27% (+1)
Conservatives 14% (+1)
UKIP 7% (n/c)
Liberal Democrats 6% (n/c)
Greens 3% (-1)

The percentage changes are from the previous ICM poll, which was (weirdly) published on Boxing Day.  So ICM are showing exactly the same pattern as YouGov, Ipsos-Mori and Survation - ie. no long-term change at all beyond random margin of error fluctuations, which reinforces the very strong impression that the SNP's enormous lead has remained absolutely stable since roughly mid-October. 
Where the firms do disagree is on the exact extent of that lead, and oddly enough ICM - who were one of the more Yes-friendly firms during the referendum - seem to have emerged as one of the less favourable firms for the SNP in the general election campaign.  The 16% gap they are suggesting is only just over half as big as reported by the last Ipsos-Mori poll in January.  It's also 3% and 5% smaller than reported by the most recent YouGov and Survation polls respectively.  (As is noted in the comments section below, some of this difference can probably be explained by ICM's highly questionable "spiral of silence" adjustment, which artificially allocates some undecided respondents to the party they voted for in 2010, thus boosting the reported vote for both Labour and the Liberal Democrats.  It may not be immediately obvious that the Lib Dems have benefited, but in fact 6% is better for them than other firms have suggested.)

However, as with the December poll from ICM, the Guardian have pointed out that, beneath the surface, the results are every bit as unforgiving for Labour as anything we have seen from any other firm.  The SNP surge appears to be much more dramatic in Labour heartland seats, and less so in seats where a smaller swing is required due to a split unionist vote.  On the face of it, this would translate to exactly the same type of apocalyptic wipeout for Labour as suggested by Ipsos-Mori, or by the Ashcroft constituency polling.  However, the breakdown by 'type of seat' is based on small sample sizes, and is therefore not hugely reliable.

As an aside, I must point out how intensely irritating it is that the Guardian's report on the poll has done what so many other media reports have been doing for weeks, and distorted the SNP's latest comment on the potential for a deal with Labour in order to paint it as something dramatic and new.  The claim is that Alex Salmond ruled out anything beyond an informal vote-by-vote arrangement at the weekend, whereas in fact he did the complete opposite - he explicitly told the Andrew Marr show that a formal confidence-and-supply deal was "possible".  He added that vote-by-vote was "probable", but that's exactly the same formulation we've been hearing for weeks.

*  *  *

UPDATE : Today's Britain-wide Ashcroft poll has the SNP on an exceptionally high 6% of the vote - ahead of the Greens, and just 2% behind the Liberal Democrats.  The Scottish subsample figures are : SNP 56%, Labour 20%, Conservatives 17%, Liberal Democrats 4%, Greens 1%, UKIP 1%.