Sound as a Pound

I'm no economist, and I'm agnostic in general on the question of Scottish independence. I don't know whether Scotland, the UK, both or neither would be better off in the event of a currency union - though for what it's worth my instinct is strongly against it, since such arrangements tend to be inherently unstable (vide. the Euro) unless accompanied by just the kind of unification of fiscal and other policies that it's point of independence to do away with. When it comes to good fences making good neighbours, I'm with Hadrian.

But I'm surprised that no one (as far as I know) in the grand coalition of Westminster parties now forming against currency union has raised the possibility of a UK referendum on the issue. I thought it was now the consensus that measures such as unifying our currency with that of a foreign power (which Scotland would then be) were exactly the kind of constitutional change that would need to be put directly to the people. If that applies to a union with the Eurozone, why not with Poundland?