A snap verdict on George Osborne's high-stakes currency gambit from Scottish politics expert David Torrance:
Isn't this a self defeating move from Osborne? Won't the sight of the chancellor in Edinburgh get the Scottish people's backs up?
"It's true and Osborne's acutely conscious this is a risky strategy, but the calculation is that the people it annoys have already decided to vote 'yes'.
"Osborne's speech was directly pitched at undecided voters. Westminster thinks that faced with a choice between what the chancellor says and what the Scottish government says, moderate undecided opinion will go with the chancellor because it's less risky.
"To be fair to the Scottish government, it could be true there's an element of bluff to this. But to dismiss it as purely a campaigning tactic is silly. This is a pretty big, important campaign, so of course there's going to be campaigning tactics.
"And if - as the Scottish government says - it's bullying then what's Alex Salmond doing with his repeated suggestion in recent years that he'd renege on UK debt?
"There are tangible problems with currency union and anyone who thinks that's not a problem needs their head examined. Bank of England governor Mark Carney said it was feasible but would come with such stringent conditions that it can't really be called independence."
But this is bullying isn't it? Isn't there a chance those undecided voters will turn into anti-English tribalists if they feel they're being pushed around?
"As in all these things it's not an exact science. I imagine there will be some that think: 'To hell with you, Gideon, you posh bastard. I'll vote independence'. As with all these things it's a trade off. Westminster is calculating that enough people will go the other way.
"In the short term it probably won't make a difference. Those undecided will continue to say that, but this will still inform how they vote come September.
"It comes to the point of credibility. The Scottish government says: 'They're just bluffing, they don’t mean it'. What do they base that on except wishful thinking?
"The wider point is it's a bit bizarre that the SNP have turned into William Hague circa 2001 saying: 'Keep the pound, keep the pound'.
"The standard SNP response is: 'Does currency union make Germany or France any less independent?' But the crucial point is they have a say on that currency. And also it's gone rather pear shaped in recent years.
"So the SNP fall back on the Belgium–Luxembourg economic union of 1921. They're comparing a city state union with a nation state. It's a completely different proposition."
We've recently seen a change in the tenor of the debate, at least in Westminster, with pro-union commentators and campaigners suddenly seeming quite panicked by the possibility of a win for the 'yes' camp. Are they right to have the jitters?
"Yeah, it's valid. It's interesting it's shifted. It was instigated by a couple of opinion polls appearing to show movement towards 'yes'. Given there has been no movement before, it's made you guys sit up and listen. But obviously you've got other distractions, like half of England being underwater.
"People I speak to in Edinburgh and London are much more engaged but mostly because it's getting nearer. It's a matter of proximity combined with movement in the polls."
David Torrance is Alex Salmond's biographer and the author of The Battle for Britain, an insider's account of the fight for Scottish independence. You can purchase the book here or click here to read an exclusive extract. Follow him on Twitter.