There has so far perhaps been something of a reluctance amongst those working on London newsdesks to accept that the SNP could emerge as the third largest party at Westminster in May, and in so doing potentially do serious damage to Ed Miliband’s prospects of winning a Commons majority. If so, that reluctance should be dispelled by the publication today of a (pre-Christmas) poll conducted (online) by ICM for The Guardian.

In itself the results of the poll (the first poll of voting intentions in Scotland that ICM has conducted for many years) are not particularly remarkable. SNP support is put at 43% for next May’s Westminster election, while Labour are on 26%. At 17 points the SNP lead is actually rather less than the 24 point one in a poll conducted by Survation at almost the same time, but published shortly before Christmas.

What, however, this poll brings anew to the evidence is an estimate of how well the parties are doing in different types of seats in Scotland. Inevitably, these estimates are based on relatively small sample sizes and thus have to be treated with caution. But what they do suggest is that there is no reason to believe that the swing to the SNP does not extend to what are supposedly the safest Labour seats in Scotland. If anything, the swing appears to be even greater in such seats. In seats where Labour is defending a majority of more than 25 points the swing in the poll from Labour to the SNP since 2010 is 24 points, rather higher than the 19.5 point swing for Scotland as a whole.

That means that, if anything, estimates of how many seats the SNP might win that are derived by assuming that the Scotland-wide movement uncovered by a poll would be replicated in each and every constituency in Scotland could actually underestimate the scale of SNP gains. In the case of this poll, projecting the Scotland-wide movement across the country as a whole produces an estimated seats outcome of SNP 45, Labour 10, Liberal Democrats (on 6% of the vote), 3 and the Conservatives (on 13%), 1. But if we take into account the difference in the movement in different types of seats then the estimate becomes SNP 53, Labour 3, and Liberal Democrat 3 (while the Conservatives emerge empty handed). In short, pretty much every Labour seat in Scotland has to be regarded as currently at risk of being lost to the SNP.

Many of the by now familiar patterns that underlie this SNP ‘surge’ are again to be found in this poll. The pattern of voting intentions for Westminster is almost identical to those for the Scottish Parliament. Indeed no less than 94% of those with both a Westminster and Holyrood (constituency) vote intention say that they would vote the same way in the two contests. At the same time those intentions heavily reflect how people voted in the referendum; in this poll 81% of those who voted Yes go on to say they will vote SNP next May, compared with just 9% of No voters.

Meanwhile what this poll particularly makes clear is the impact that this alignment of Westminster vote intentions with referendum vote has had on Labour support. Amongst those who say they voted Labour in 2010, 34% say that they voted Yes in the referendum. No less than 68% of this group of Yes voting 2010 Labour supporters now say that they will vote SNP in May. Just 28% remain loyal to Labour. In contrast no less than 87% of those 2010 Labour voters who voted No in May are still backing the party.

Not least of the reasons why the presence of a large group of SNP MPs at Westminster could make the formation of a stable government difficult in the event of a hung parliament is the party’s commitment to scrapping Britain’s nuclear weapons facility, something that the party leader, Nicola Sturgeon, has suggested could be a red line issue for the party in any post-election negotiations. Today’s poll confirms the evidence of the Scottish Social Attitudes survey that amongst Scots as a whole those who would like to see Trident scrapped (43%) are slightly more numerous than those who would like to see it maintained (37%). But this is an issue on which those who say they will vote for the SNP next May take a very different view (77% want it scrapped) from those who propose to vote Labour (22%). Indeed, it is a topic on which those who voted Labour in 2010 but voted Yes in September (72% want it scrapped) have a different stance from those who voted No (19%). It may well be the case that the referendum has not only ensured that the constitutional issue is now playing a more central role in Scotland’s electoral politics, but that it has also helped propel the importance of the nuclear weapons issue too.

Apart from providing yet further evidence of Labour’s woes north of the border, today’s poll also gives us evidence, further to that previously provided by YouGov, on how people in Scotland view the proposals of the Smith Commission. It confirms the impression created by that earlier reading that those who back the proposals have a lot of work to do to persuade voters of their merits.

First of all, it appears that many voters are none too sure either way about the proposals; as many as 31% say that they just do not know whether the proposals went too far or not far enough, perhaps because ICM used a wording that (unlike YouGov’s) acknowledged that respondents might not have heard much about them. Meanwhile, even though respondents were advised that the proposals entailed ‘extensive new powers over income tax’, those who say the proposals are ‘about right’, 26%, are still outnumbered (albeit less so than in YouGov’s poll) by those (30%) who think they ‘do not go far enough’. At the same time another 13% feel they ‘go too far’. Only 12% of those who voted Yes in September believe the proposals are about right, suggesting their unveiling has so far done little to erode support for independence. But even those who voted No in September give the package a pretty lukewarm reception; only 38% think the proposals are about right, not much more than the combined proportion of those who think they go far (22%) or not far enough (9%).

For some at least, one of the perceived limitations of the Smith proposals is that they do not provide for the devolution of corporation tax. Advised that Smith proposed to devolve income tax but not corporation tax, no less than 53% said that the tax on business profits should be devolved, while only 23% said it should not. These results reflects the findings of many a previous poll. Even Labour supporters are almost evenly divided (33% are in favour, while 38% are opposed) even though their party has taken a tough stance against devolving the tax.

However, those who think that devolving tax would open the path towards higher taxes and spending north of the border may need to think again – as indeed might those such as the Scottish Conservative leader, Ruth Davidson, who hope to be able to reduce devolved taxes. Only 26% of all voters think that taxes should be raised in Scotland in order to spend more on services north of the border, and even with the ranks of SNP Westminster voters that figure is no more than 41%. Equally, however, just 13% think that spending should be reduced in order to cut taxes, and even amongst Conservative voters only 20% are of that view. No less than 41% think the current balance of taxation and spending should be retained. Any future Scottish government that proposes using its devolved tax powers to increase or reduce taxation and spending could well have a considerable battle on its hands.