With exactly one week until the Scottish referendum, the latest polll has put those against independence six points ahead of those for. Yet just earlier this week, the Yes campaign was two points ahead of the Better Together movement — its first time leading the race. The edge in the polls prompted the leaders of the three main British political parties to head to Scotland to campaign for the integrity of the United Kingdom. In a speech yesterday, Prime Minister David Cameron implored Scots “fed up with the effing Tories” — his own political party — to remember that this referendum has further implications than a general election. Yet, in his emotional address, Cameron failed to reiterate the conservatives’ position on Scotland keeping the currency of the United Kingdom.

In February, all parties said they would not allow an independent Scotland to keep the pound. Since then, the conservatives have not focused in on the very real possibility that Scotland will be without a currency, which is perhaps the Better Together campaign’s strongest argument. The Scottish government believes it can both secure EU membership before becoming fully independent and retain the pound. This is in spite of a recent statement from Bank of England governor Mark Carney that “a currency union is incompatible with sovereignty,” and Chancellor of the Exchequer George Osborne declaring that “if Scotland walks away from the U.K., it walks away from the U.K. pound.” In addition, Scotland must reapply to the EU, and a representative has said it “would simply not be possible” for an independent Scotland to keep the pound and join the EU.

There are certainly other important factors  in Scotland’s vote on independence, such as its tendency to lean further to the left on political and social issues, a dislike of nuclear weapons and a desire to keep oil funds within Scotland. The pound is in no way the deciding factor, but it is the unionists’ most important argument. By failing to stress its importance, Cameron has not only let his own side down, but also all voters in Scotland.

Yesterday, Scottish First Minister Alex Salmond once again challenged  Cameron to a debate, after his previous attempts months ago were rejected. It is high time the prime minister takes his position as the head of a union seriously and gets involved in the real debate, not the debate that exists within Westminster. If Cameron backs his party’s stance that Scotland cannot keep the pound, he needs to come out and say so instead of leaving voters wondering what will happen economically. Scotland needs a real mandate, not a vote based on economic hopefulness, and Westminster has a duty to clear up the confusion.

A version of this article appeared in the Thursday, Sept. 11 print edition. Email Tess Woosley at [email protected].