During last week's currency wars I was reminded of something Grant Baird, once Alex Salmond's boss at the Royal Bank of Scotland, said when his protégé was first elected to parliament in 1987.

After praising his ability to generate "favourable publicity" relating to the bank's oil interests, Baird added that Salmond "perhaps had a less sure touch on purely financial matters". But, he concluded, "he has a very cool head and the ability to play a long game".

It wasn't a bad description of Salmond the politician either. His handling of the media, unflappability and strategic skill have always served him well, and while he derived a lot of economic kudos from his background (St Andrews, RBS) his financial nous has always been more rhetorical than real, thus his ability to sound persuasive even when the detail made little sense.

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Context was also crucial. As the leader of a small opposition party Salmond's ability to "hold the line" on a particular policy was relatively straightforward, and even as First Minister from 2007 the detail of his independence proposition received relatively little scrutiny. But since 2011 the dynamic has changed: everything now posited by the Scottish Government is examined as never before.

Which, in a roundabout kind of way, brought us to the events of late last week. The "currency union" policy had never been particularly convincing, so full of intellectual contortions and over-triangulation. Such an arrangement, we were told, was in the "best interests" of both an independent Scotland and rUK; not only were their economies virtually identical but cross-border trade made it virtually a necessity.

Unfortunately the logical conclusion of those arguments was not independence but the status quo, or at most a reformed version of the status quo. The SNP's response to the Unionist parties' triple block was similarly muddled, with Salmond warning of an "Osborne Tax" on English businesses. If the First Minister is seriously concerned about uncertainty, disruption and financial sector jitters, then why on earth is he pursuing independence at all?

But then the SNP's currency union policy was not forged on the basis of economics, rather it was a political - or more accurately a tactical - decision. Faced with a choice of the euro, a Scottish currency or the status quo, the last of those emerged as the best of a bad bunch. For that reason alone it was never sustainable, and while before 2011 no one really noticed, under the unforgiving gaze of the referendum it held for a while and then withered.

This morning the First Minister will stand before an audience in Aberdeen - a location chosen to illustrate how much sterling "needs" Scotland - and proclaim, Iron Lady like, that he isn't for turning. Salmond will assure Sir Nicholas Macpherson that his plans for a sterling zone are not temporary, directly contradicting elements of Yes Scotland who, according to recent reports, want to prepare precisely that contingency. There will be no Plan B.

Salmond isn't alone in hardening his stance, for the President of the European Commission has now gone from diligently avoiding direct reference to an independent Scotland, to warning unequivocally that it would be "extremely difficult, if not impossible" for it to join the European Union. "Independence in Europe", of course, was the first plank in the SNP's derisking strategy, and it too is coming under increasing pressure.

Yes Scotland strategists see the two issues - currency and Europe - in a similar light. The Chancellor and the Commission President, they argue, are simply playing politics, and that following a Yes vote both will change their tune, paraphrasing the old Mandy Rice-Davies defence: "Well they would say that, wouldn't they?" But even accepting that, it leaves pro-independence campaigners with an obvious problem: convincing undecided voters to accept their word over that of Messrs Osborne and Barroso.

That will, to say the least, prove challenging, for whatever Scots think of those two figures, they do not generally share the Scottish Government's disregard for their thoughts on the relative merits of a currency union and EU membership. Salmond et al can hit back with reference to the deliberations of the "Fiscal Commission", but the trouble is that punters have never heard of that august body, whereas "the Treasury" is a familiar (if unloved) entity they generally take seriously.

And undecided voters are the key group in all of this. Judging by the unscientific measurement of Twitter, Osborne and Barroso's interventions have made a lot of Yes voters even more determined to vote Yes, and although Better Together are bracing themselves for a short-term hit in the opinion polls (they believe the "bullying" line will resonate for a while), it's difficult to believe that by September the Treasury and European Commission will somehow have become so thoroughly discredited that they will have ceased to be relevant.

Once again, meanwhile, SNP and Yes Scotland voices have appeared shouty and shrill in response to interventions from London, and while that plays well to the converted, it does little to win over those yet to make up their minds. It has also highlighted once again the tension between rhetoric and reality when it comes to the SNP's view of independence. While the White Paper and Independence Declaration give the impression of undiluted sovereignty, the detailed policy tells a rather different story.

So while Alex Salmond might repeatedly assert that the "days of Westminster politicians dictating to Scotland are over", that's precisely what a currency union would involve. As Sir Nicholas observed in his letter, if "the dashing of Scottish expectations were perpetually blamed on continuing UK intransigence within the currency union, relations between the nations of these islands would deteriorate".

That hit the nail on the proverbial head. In a speech at University College London last week, Nicola Sturgeon love-bombed the UK capital and said she didn't want an independent Scotland to end up "sitting on the periphery" and "girning" about London, but a currency union - assuming it happened - would lead to precisely that. The Bank of England would become a proxy for Westminster rule.

But such is the consequence of arguing that independence will change everything while at the same time keeping everything pretty much the same. When it comes to the monarchy this is credible enough, on EU membership almost believable, but less so in terms of currency, energy and university research funding. Repeating mantra like that "common sense will prevail" in all those areas simply doesn't cut it.

"It's not going to change," one pro-independence source told me of the position on currency and the EU. "It's not going to change in the next seven months - we'll hold the line."

But holding the line is no longer as easy as it was when Alex Salmond first entered the political arena in 1987, or even immediately after his electoral triumph in 2011. Suddenly the politics of independence are real, and credibly holding the line will take a lot more than repetition.