Now that people drum their fingers impatiently when an ATM in Thiruvanathapuram or Nonthaburi takes more than five seconds to cough up, in the local currency, money from their bank account back home, it's easy to forget that until fairly recently, large chunks of overseas trips were devoted to the exchange of currencies.

Even though the electronic transfer of funds has made that a thing of the past, there are still plenty of countries where many traders would prefer that you didn't pay in the local currency, but in sterling, euros or dollars (in Turkey, for example, the visa for entry which you get on arrival, can only be paid for in one of those currencies, not in Turkish lira).

And there are a few countries which use a currency issued elsewhere, and over which they have no control; in Panama, the US dollar is an official currency, alongside the balboa. The balboa is, in any case, pegged to the value of the dollar, as the Lithuanian litas used to be (it's now pegged to the euro).

In the mid-1980s there was no need to change British money to punts if you were visiting Dublin, since sterling was just as readily accepted – though you lost on the deal, because the punt was then worth about 90p, but pubs and restaurants operated as if they were equal. And you invariably got your change in Irish money. At the time, the Irish were scathing about their economy ("I'll tell you the price of Irish republicanism – £1.65 a pint!"), though they may now look back at those prices, and that currency, more warmly, given the chaos the euro brought them.

I mention all this to emphasise that money is, at root, a mechanism for exchange and a store for value and that people who buy and sell things will do so in any medium they trust. If Scotland chooses to become independent, those people will work out (officially or unofficially) how to carry on doing that. The choice of currency which is made may improve matters or make them worse, but there's no sure way of knowing which because there's no sure way of knowing anything about what hasn't happened yet.

But though we can only make informed guesses about whether an independent Scotland's economy would prosper or flounder, we can be sure of one thing about its currency. Unless it adopts and issues its own, it will not control it. Sovereignty inheres in the power to issue money, and if Scotland adopts the euro or sterling it will not control that. In the most wildly optimistic scenario, it might have a minority say in monetary policy, but it's more likely it would have none or practically none.

And yet the First Minister has taken the Chancellor of the Exchequer to task because he has pointed out this incredibly obvious fact. What was most interesting about Alex Salmond's attack, though, was that he focused on listing every negative point he could think of about the Chancellor (something many of us would not find an arduous or unpleasant task) except the point which he was actually making, which he neglected to address at all.

If the eurozone has made anything apparent, it is the fact that financial union without political union is about giving up control. So the current argument of the Yes camp for using sterling in an independent Scotland is – no matter whether it would work well or not – self-evidently an argument for less control of monetary policy than we have now. It is like arguing that you'll actually be able to drive the car better from the passenger seat.

But Mr Salmond didn't mention any of that. Instead he pointed out that the UK's credit rating has been downgraded – something Mr Osborne has made a priority of avoiding – and that we're still (at best) on the brink of recession. The First Minister's position on the currency may be utterly incoherent, but at least this analysis (though it has nothing to do with the point at issue) is straightforward. It can be summed up by saying Mr Osborne isn't much cop.

Mr Salmond is far from alone in this belief, which has been bolstered in the past week by the discovery that an economic paper much cited by the Chancellor as a basis for his policies contains an arithmetical error. Critics have gleefully seized on this fairly embarrassing discovery, and the failures in the recovery that the First Minister mentioned, as proof that Mr Osborne is useless and austerity is counter-productive.

Well, yes and no. Yes, Mr Osborne is useless but, no, it doesn't prove austerity is slowing growth. We can know that for a certainty because the chief reason for thinking Mr Osborne is useless is that he hasn't tried any of the austerity he keeps going on about. The economists who claim austerity in a recession slows growth are as vocal now as they were after the Budget of 1981, when 364 of them wrote a letter claiming monetarism was misguided, just days before the economy began growing and proved them all wrong.

But this time the Chancellor can't prove them wrong because he hasn't, unfortunately, done what he has been accused of. I'm getting tired of saying this, but nobody seems to believe it. Public spending is going up. Benefit spending is going up. Government borrowing is going up. The ratings agency Fitch now expects the national debt (still going up, naturally) to peak at 101% of GDP in 2015-16, which is why it downgraded Britain the other day.

Meanwhile, what happened to the huge reduction in the public sector, the "bonfire of the quangos" and all the other measures trumpeted when the Coalition was first assembled? How is anyone to know whether austerity will make matters worse? Because whatever the Chancellor thinks he's doing, it certainly isn't austerity.

The truth is that, with minor adjustments, Mr Osborne has essentially adopted the economic plans which Alistair Darling had already laid out, which may account for why, despite the scorn he pours on the Chancellor, Ed Balls goes strangely quiet when asked to spell out in what way his own policies would differ from the Government's.

In the face of all these unpleasant facts, it seems a little pointless to be arguing over the nature of some hypothetical future Scottish money. Because, as Liam Byrne, Labour's former Chief Secretary to the Treasury, pointed out, there isn't any money. There's just a huge great pile of debt.