Guardian/ICM poll finds support for no campaign on 51% and yes on 49% with less than a week to go, but 17% of voters say they have yet to make up their mind

The union between Scotland and England hangs by a political thread as a fresh Guardian/ICM poll published on Friday puts the yes vote just two percentage points behind those supporting no.

Despite a week of intense political campaigning by pro-union politicians and repeated warnings from business about the dangers of independence, the poll finds support for no on 51% and yes on 49% once don’t knows were excluded.

The Guardian/ICM poll is based on telephone interviews conducted between Tuesday and Thursday, the first such survey ICM has conducted during the campaign. Previous polls suggesting that the race for Scotland could go to a photo-finish have been based on internet-based surveys.

In the UK-wide referendum on the Alternative Vote in 2011, a similar Guardian/ICM poll predicted the final outcome with remarkable accuracy.

The period of the survey not only witnessed the three UK party leaders absenting themselves from prime minister’s questions to campaign in Scotland, but also a growing rumble of news stories about the economic risks of independence: Mark Carney, the Bank of England governor, gave new warnings over the currency, some financial institutions such as RBS signalled readiness to move their headquarters out of Edinburgh, and there have been warnings about a mortgage drought.

Despite all of this, and the most recent suggestions that supermarket prices could have to rise, everything remains to play for in the final days of the campaign, because 17% of voters in the overall sample say they have yet to make up their mind. Including them in mix, the rounded figures leave yes on 40%, and no on 42%.

The unprecedented political engagement generated by the campaign shines through in the poll, which finds 87% of respondents describing themselves as “absolutely certain to vote”, far more than the 55% who said the same thing about the next Westminster election in the most recent UK-wide Guardian/ICM poll.

Most unusually, young people are almost as engaged as their elders, with 82% of 16- to 24-year-olds and 87% of 25-34s insisting that they are 10 out of 10 sure that they will cast a vote; many will have already done so through postal voting.

The 25-34s in particular are heavily inclined to back independence – leaning yes, by 57% to 43%. At the other end of the age range, respondents aged 65+ are staunch unionists, being inclined to vote no by 61% to 39%, a contrast that – Martin Boon, director of ICM explains – makes “the generational divide a crucial dividing line in Scottish politics right now: each campaign’s success in motivating the particular cohorts that favour them looks crucial to the outcome”.

Boon explains that the salience of age makes including the right generational mix in the sample especially important, and suggests that Friday’s poll looks as good as any on this count. “All polls, whether conducted online or by phone, struggle to interview a representative number of young people. However, unusually, ICM have managed to interview close to the right number, which avoids unhelpfully high levels of weighting, and helps us pin down the real link between age and indyref voting intentions.”

Sex is an important secondary faultline – excluding don’t knows, Scottish women remain loyal to the UK, by 55% to 45%, while Scottish men by contrast are, by 52% to 48%, in favour of independence.

Gordon Brown’s intervention on behalf of the unionists in recent days has aimed at luring Labour’s core supporters back towards the no camp, amid a sense that they had begun to drift away, particularly in the west of Scotland. The party will be relieved that Glasgow remains – just – inclined to vote no, by 51% to 49%, but broader west and central Scotland are leaning narrowly towards yes.

Only 29% of those who stuck loyally to Labour in Alex Salmond’s landslide year of 2011 say they will vote for separation, a somewhat lower proportion than that which has been found in some of the internet polls. But look instead at the much larger proportion of Scots who voted for Brown in 2010, a respectable year for the party north of the border, and crumbling of the broader Labour family becomes apparent. Forty-two percent of these voters are now signalling that they will vote for Scottish divorce from the UK. By contrast, the SNP vote is more solidly behind yes: 91% of those who voted for Salmond in 2011 intend to follow his lead again, and vote yes.

Friday’s poll also interrogates what is motivating supporters of the two camps – asking respondents to choose the two or three issues that incline them to vote as they intend. Among no supporters, feelings towards the UK are the single most important factor – named by 53%, followed by 37% who suggest that continuation of the union would be better for Scottish pensions and public services. Economic fears of separation, the principal focus of Better Together campaign over most of the course of the year, rank as less important, nominated by just 33% of nos.

On the yes side, the single most important factor are feelings about Westminster’s politics, which is named by 51%, while 40% express the hopes that independence would deliver a more prosperous future. Despite a recent emphasis on the risks of English-inspired NHS privatisation, among yes supporters feelings about public services and pensions are less important – identified as especially important in determining their decision by just 24%.

Asked “how risky” they think independence is, little more than a quarter of Scots (26%) say it represents “a huge risk”, considerably more than the 13% who believe that it is “no risk at all”, but less than the 56% who rank the dangers as somewhere in between the two. Sticking with the UK is, not surprisingly, seen as a safer option – only 19% regard that as “a huge risk”, as against 32% who rate it as “no risk at all”. The difference between the two propositions as measured by the average scores on the five point riskiness scale (where 5 represents a huge risk) is substantial, but not perhaps as large as might be expected. The mean score for sticking within the union is 2.7, compared with 3.2 for going it alone.

ICM Research interviewed a representative sample of 1,000 people by telephone on 9-11 September 2014. Interviews were conducted across Scotland and the results have been weighted to the profile of all adults. ICM is a member of the British Polling Council and abides by its rule