Is the opposition of the three main political parties at Westminster to a post-independence currency union with Scotland a bluff? North of the border, many believe it is. I have no window into men’s souls: these Scots may be right.

But I hope it is no bluff. A currency union does not have to be ruled out on any terms. But a union that could make sense for the rest of the UK would be highly unequal. Why would a newly independent nation accept it?

Experience with the euro has clarified many issues relating to currency unions. Some are only partially relevant to a currency union between Scotland and the rest of the UK. While the oil-dependent Scottish economy would be different from that of the rest of the UK, it is fair to argue that, after more than three centuries, integration of the economies and, in particular, the labour markets, is sufficient to make currency union workable. This, after all, is an old and successful venture.