James Cartlidge is Director of Share to Buy and a Babergh District Councillor.

Labour’s 1997 manifesto famously promised to support Britain’s membership of the euro subject to the passing of five economic tests, but only if the people of Britain said “yes” in a referendum. In the 2001 general election, William Hague warned that there were only “twenty-four hours to save the pound”. He could say exactly the same thing on the morning of the Scottish referendum on whether or not to remain in the UK – if, that it Scotland votes to leave and a so-called ‘Sterling Zone’ of independent sovereign nations is formed.  For this would not be a case of the current currency remaining unchanged. In such an eventuality, not just Scotland, but the rest of the UK would be joining fundamentally new currency arrangements carrying the same potentially catastrophic risks as membership of the euro did, and still does.

It matters not that our coinage would still look the same – a post-independence Sterling Zone would be a new currency for Wales, Northern Ireland and England as much as it would be for Scotland. As with the euro, all the British nations would be entering into a currency zone comprised of independent sovereigns. The experience of the Euro established a precedent: for Britain’s currency to change, there must be a referendum of all the people of the union.

Now, some have alluded to the possibility of such a referendum if Scotland votes to leave; there have been hints from HM Treasury that such an arrangement would “never happen”. But in this age of political scepticism about referendum promises, hints are surely not good enough. Can we imagine the impact it would have on the Scottish referendum debate if, next week, the Prime Minister stood up in the Commons and announced that the people of England, Wales and Northern Ireland would be offered a referendum on the day of the European elections that asked:

“If Scotland votes to leave the United Kingdom, should Scotland be able to keep pound sterling as its currency?”

As with any referendum question, there would need to be considerable care and consideration of the exact wording – but the sentiment is clear. Democracy in the Union cannot be restricted to a relatively small part of the total population when it comes to determining the fundamental future of our economy. There may be many in Britain outside Scotland who do not want it to leave the Union, but who, in the event of a vote for independence, would nevertheless think it best for commercial reasons to have a Sterling Zone.  However, I cannot help but think that the pain in Spain and Greece might just be enough to persuade voters outside Scotland that such a prospect was a huge risk.

Timing would be an interesting issue. If such a referendum were held in May, Scotland would vote in the referendum knowing where it stood – since a ‘no’ vote in England, Wales and Northern Ireland would surely consign the prospect of a Sterling Zone to oblivion, and ensure that an independent Scotland would have to man up and take genuine responsibility for its future outside the Union by forming its own currency or deciding separately to join the euro.

However, on the assumption that May would be too early and therefore impracticable, there would be the interesting possibility of holding the referendum on the same day as the Scottish one.  This would have the huge benefit of ensuring that the debate building up to judgement day would occur across Britain, involving all its people. More realistically, the referendum could happen on the same day as the general election in 2015. In this scenario, Scotland would go into the independence referendum with the certainty that, in the event of a vote to leave the UK, it would have to wait on the rest of Britain before determining its economic future, an entirely proper scenario given that every single subject of the Union would be profoundly affected by the implications of Scotland divorcing with its credit card still underwritten by the former spouse (the arrangement otherwise known as a Salmonesque Sterling Zone).

This in turn would add to the huge uncertainty of the outcome of a ‘Yes’ vote in Scotland, thus crystallising unambiguously the reality of the choice before Scotland in October – that leaving would entail huge uncertainty and might require a new currency or the euro, and therefore represents a risky move. Above all, a debate that has most often seemed to be about just Scotland – or occasionally Scotland in relation to England, but never about Wales and Northern Ireland – would by definition have to involve every nation of the Union including, as equal partners, its two western members.

Some might argue that we have enough referenda to worry about, not least with a potential vote on EU membership. Yet, under any scenario, this is not imminent; on the other hand, it is a fact that the Scots will vote in October and that if they vote to leave, a Sterling Zone ‘fait accompli’ could be on the cards within months, with our negotiating position undermined by the tide of newly-made history. As it happens, we have already crossed the rubicon on Europe: we didn’t join the euro, and that has and will continue to determine an inevitably separatist course for us in the future, come what may. Yet having avoided one currency union, are we really going to sleep walk into another?

One lesson from history is perhaps paramount – in the end, a referendum on Britain’s membership of the euro never happened. The economics were never right; the five tests never passed. A Sterling Zone referendum in England, Wales and Northern Ireland, timed for May 2015, would be entirely conditional on a ‘yes’ vote for independence, and would also – hopefully – never actually happen. But the prospect of such a plebiscite, a granite-defined indisputable commitment to the principle of all the Union’s nations settling all of the Union’s economic future, might resonate powerfully throughout the land and reaffirm the principle that no nation should be left bereft of a voice in deciding the future of our economic fundamentals. The peoples of England, Wales and Northern Ireland deserve no less.