The Scottish independence debate just got interesting. Not over the future of North Sea oil or nuclear submarine bases, but on the dull matter of monetary policy.

In September, Scotland holds a referendum on whether to remain part of the United Kingdom or go solo. So far, many people just assumed that a 'Yes' vote would be crazy. Scotland already has devolved government, with its own Parliament in Edinburgh deciding matters such as health, education and welfare policy. Scotland has more than its share of MPs in the UK Parliament in London, who even get to vote on exclusively English matters. It also enjoys a higher share of UK public spending. Devolved powers and English subsidies...seems like paradise.

The polls reflected the strength of this 'No' case – but things are narrowing. The Scottish nationalist leader Alex Salmond is a wily politician. His party won a majority in the Scottish Parliament despite an electoral system designed to keep them out. He tells Scots not to throw away their one chance of doing something extraordinary. He affirms Scotland's proven ability to run its own affairs. And he makes the point that an independent Scotland would never have to endure a Conservative government ever again.

By contrast the 'No' campaign looks unambitious and condescending, suggesting that Scots aren't up to governing themselves. And the Conservatives, mostly pro-union, have such a polluted brand in Scotland that they kept quiet rather than adding weight to the 'No' lobby.

Brave, then, for Conservative Chancellor of the Exchequer to enter the fray, saying that an independent Scotland would not be allowed to keep the pound sterling. Nonsense of course: only draconian laws preventing cross-border sterling business could stop that. And with so much cross-border trade, forcing Scotland into a new currency helps neither country – though that is what Osborne is trying to imply.

The reality is that the Scots could use the pound (or for that matter the dollar, euro or yen) but would have no say in the currency's management. But Osborne insists that the Bank of England would set interest rates and create money according to the needs England, Wales and Northern Ireland – not some foreign country called Scotland. Again, that is over-egging it: with so much cross-border trade, the Bank would have to take account of conditions in Scotland when setting its policy.

So the Scots would be like Ecuador, Panama or El Salvador, who use the dollar but who have no voice in US Federal Reserve policy. And just as they have no hope of the Fed bailing them out in a crisis, Scotland cannot expect any Bank bailouts either. That sounds bleak until you remember that Panama's banks are some of the world's soundest. They have to have big reserves precisely because there are no bailouts. So that might even make Scottish banks more attractive in these uncertain times.

Up to a point. The Scottish banks, or government, would still have to create a financial buffer big enough to ensure that Scotland's financial sector can keep standing without Bank of England support. It is a big ask: the Royal Bank of Scotland alone would need billions of new capital to let go of the Bank of England. Where does the money come from? The worry is that Scotland's huge financial sector would up sticks and head south, where it could still cling to nurse. And that anyone left behind would have to offer investors sky-high interest rates to reflect their risky go-it-along policy – which they would in turn have to pass on to borrowers, like people with mortgages.

The wily Salmond will have some answer, of course. The pity is that we have not had this rather critical debate until now. It would certainly have made the whole campaign a lot more interesting.