OPINION polls should be taken and not inhaled, but this week's Mori poll showing a doubling of support for independence among 18-24-year-olds is intriguing.

This is the group that the Yes campaign has been stalking with its social media and networking techniques. Young people tend to get much of their information from Facebook and Twitter (often plagiarised of course from the press). They rely more on word of mouth than messages from above. They are also the Holyrood generation, who have grown up with the Scottish Parliament part of their psychological landscape and have lived much of their adult lives under a Nationalist government.

Mind you, the under-25s are also the people least likely to vote in elections. Which is why the No campaign doesn't seem particularly worried by the Mori/Times poll, even if it is accurate. They are pleased by the strong support for the Union among other age groups and particularly among women. 61% of women say No, according to Mori and 55% of all age groups would vote No, against 34% who would vote Yes. There is a gender gap opening over independence. The better-off are also less likely to vote Yes – so it looks like the Nationalists need to do some missionary work among middle-aged women's groups in Bearsden and Milngavie.

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It's been a good week for statements of the bleedin' obvious, so let's just point out again that this is one poll, and the only one that matters is still 20 months away. In some ways, what is more interesting is the continuing popularity of the SNP Government in Holyrood. That Alex Salmond retains a positive approval rating of +7 after having been in office for nearly six years is remarkable. David Cameron, by contrast, has a negative rating of minus 40. Also, the number of Scots who say they would vote SNP for Holyrood is at much the same level as in the 2011 election. Which means that, on these figures, if an election were held tomorrow, Alex Salmond could be back as First Minister with another landslide. That's astonishing, after six months in which he's been generating such negative headlines in the press over matters such as the legal advice on EU membership.

Perhaps there's a message buried here for the No campaign and Labour. Their campaigning has focused relentlessly on Alex Salmond's alleged untrustworthiness, and on a series of "process" issues like the mechanics of EU membership after Scottish independence. Going for the man and accusing him of being a "liar", as Johann Lamont has been doing, is always liable to backfire unless you can actually prove that he has been lying. Similarly, raising fears about Scotland being thrown out of the EU only works if there is some foundation to the claim. Yet this week the UK Government's own legal adviser, Professor James Crawford of Cambridge University, admitted on BBC Radio that Scotland already fulfilled the requirements and the Scottish Government's timetable for EU renegotiation was "realistic". The headlines about Scotland having to negotiate 14,000 separate treaties also turned out to be the usual concoction of speculative half-truths.

The claim that Scotland would not be allowed to use the pound after independence is similarly shaky. There are many reasons for not supporting independence, but the idea that the Bank of England would refuse to allow Scotland to use the common currency both countries have been using for 300 years is not one of them. As the Scottish Government's Fiscal Commission pointed out this week, forcing Scotland to use a different currency after independence would involve so much hassle for UK companies, the Bank of England and the high street banks that no-one in their right minds would seriously consider it.

There is a theoretical possibility of course, that the UK Government could be so malign and childish as to behave this way. But how does it help the Unionist case to suggest it? It's like the claim this week that Scotland had been "extinguished" by the 1707 Acts of Union, which was endorsed by the Tory Minister and Better Together spokesman David Mundell. Apart from being nonsense, this made it sound as if the Unionists wanted to wipe Scotland off the map. Yet Winston Churchill himself always argued that Scotland was a nation, a partner in the Union.

It is the same with Europe. No-one seriously believes that the European Union would try to prevent Scotland remaining in the EU after 20 years of having being subject to European law. What possible reason could Brussels have to behave so irrationally? Why risk losing a country like Scotland with prodigious energy reserves? The EU has spent decades trying to persuade Norway and Iceland to join, for heaven's sake.

Why do the Unionists persevere with these attacks? Perhaps because they get a ready response in the press in Scotland. Prof Crawford's warnings about the legal difficulties of becoming independent, contained in a UK Government position paper, received front page treatment on Monday, but his admission on Tuesday that he agreed with Alex Salmond did not. Measured on column inches, therefore, Better Together is streets ahead. But the real debate is only just beginning. Not only do a lot of Scots not believe these scares, the under-25s don't even read about them, because they are turning away from the conventional media.

There are far better reasons for opposing independence than the timetable for EU membership anyway. I could think of a dozen positive arguments for remaining in the UK. As neighbours on this small island, Scotland and England are always going to have to collaborate on a whole range of issues, from the national grid and the roads network to defence and foreign aid. If Scots are affected by decisions taken in Westminster, in the new improved UK, why should Scotland not want to be represented there, just as it is represented in the European Parliament?

No, you should always treat opinion polls with caution, because they only offer a snapshot of public attitudes. But nor should their message be ignored. The Unionists are persevering with a negative and punitive approach that has failed to damage Alex Salmond in successive Scottish Parliamentary elections, and is not being listened to by many young voters in the referendum campaign. Time to rethink.