The first votes have been cast in the referendum on Scottish independence.

Yet, with only three weeks to go before the remainder of the Scottish electorate goes to the polls, we still do not know what independence would mean for Scotland.

Alistair Darling and Alex Salmond, the two principal protagonists, have slugged it out on television. Both are still standing, out and about on the campaign trail, Mr Darling asking questions and Mr Salmond making assertions.

Of course, it will not all come down to money. There will be lifelong nationalists, wanting to break up the UK, who do not care about the economic consequences and future opportunities. They want constitutional change regardless of the uncertainties and future risks.

They say they want control over their own affairs, an admirable ambition. But what does that mean? It is not an unreasonable question to ask. It deserves an answer based on fact, not wishful thinking.

Arguments about the pound will prevail and so they should, however boring and mundane they might seem. At present, the UK has one of oldest, strongest and most stable currencies in the world. It is trusted around the world, and it is not in danger.

Although the nationalist camp is divided on the wisdom of a currency union, its refrain is that a Yes vote would give the Scottish Government a mandate to secure a currency union with the rest of the UK.

That is not the case.  It will give the First Minister a mandate to seek a currency union. To get a mandate from the rest of the UK,  the millions of taxpayers in England, Wales and Northern Ireland who now prop up the Bank of England should be asked. 

Not least, it would be good manners. To secure a mandate from the rest of the UK, the millions of taxpayers in England, Wales and Northern Ireland who prop up the Bank of England should be asked. This would be good manners at the very least.

 

As every indication to date suggests, there will not be a currency union, Mr Darling has to ignore the groans and keep pressing the First Minister on a Plan B. If and when an answer is forthcoming, the electorate can make an informed and sensible decision.

Until then, it is being asked to make an unfathomable choice. Mr Darling's critics want to hear more about his views on solidarity and workers' rights, his vision for the future. In an ordinary political campaign this would be an admirable and quite correct question, but this is not a general election debate.

It is about the constitution, and the only ideology at stake is between those who are for and those who are against separation.

It might be an inconvenient truth but barriers and borders have done little to advance solidarity, workers' rights, the welfare state, the NHS and every desirable progressive measure.

Mr Darling believes Scotland can enjoy the best of both worlds, pursuing desired, distinctive policies in the Scottish Parliament while enjoying the strength and security of the UK. In the next 21 days he should not deviate from that position.

If Mr Darling became more prescriptive, he too risks being guilty of making assumptions that are not his to make.The Scottish Parliament should establish Scotland's priorities, whether in education, hospitals, policing and every other devolved area.

What he can do with credibility is argue for what he thinks is best for Scotland and that is sticking with the pound, secured by all the taxpayers in the UK.

Scotland, in the event of a Yes vote, would fall into the category of a foreign land so he must stick to his guns to argue that Scotland's interests would not be best served by having its rates set by another country, whether it is the rest of the UK or the eurozone.

And he needs to carry on pointing out why it would not be in the rest of the UK's interests to take on the risks of another country's debts and banks.

Sir John Gieve, a former Bank of England Deputy Governor, has already said he could not see any real reason why it would be in the rest of the UK's interests to agree to a formal currency union on anything other than exceptionally controlling terms.

He might be right; he might be wrong. But one thing is absolutely certain: at present we do not know.