THE Better Together campaign has many faults.

It is tedious, piecemeal, relentlessly negative, and a factory for an endless supply of scare stores.

Although these qualities do little to make a positive case for the union, there are some signs that they are effective.

Last week was a case in point, as the putative currency of an independent Scotland moved to the fore of the referendum debate.

First there was a lurid tale about Scottish banknotes disappearing, then a slanted Treasury analysis about possible obstacles facing the SNP's plan for Scotland and the rest of the UK to share the pound. It would be the Eurozone in miniature, we were told, with the rest of the UK in the role of mighty Germany and Scotland another dysfunctional minnow like Cyprus.

George Osborne even pitched up in Glasgow to suck his teeth and furrow his brow at the thought of a sterling union after a Yes vote, though he never actually ruled it out.

There were no killer facts, no knock-out blows putting a currency union beyond the pale. Instead, Better Together said the SNP had a host of uncertainties to explain.

Not because it wanted answers, but because it wanted to bury the SNP in questions.

The tactic is Better Together's trademark. It has given up any pretence of positive campaigning, and instead tries to seed doubt through insatiable queries about ever changing issues. It is a cold and simple approach.

The SNP response was to point out that if the UK refused a currency union, North Sea oil and gas would no longer count towards the UK's balance of payments, undermining the pound. In the real world there is no chance of Westminster refusing an independent Scotland the use of sterling.

Nevertheless, the debate played into Better Together's hands. Debating independence this way, as a series of fragments, is like looking at it through a kaleidoscope – the big picture gets lost.

The SNP and Yes Scotland are now in danger of becoming bogged down in this unwinnable Q&A. Even if they could neutralise the doubts sown by Better Together, that in itself would not be enough. If they are to break out of a depressing cycle of defensive reaction, they need to articulate a clear, bold, joined-up vision of the kind of society Scotland could become. A vision built on optimism and hope rather than fear and timidity.

Only then will the momentum they need begin to build.