A YES vote would have a damaging impact on the economies of both Scotland and the rest of the UK, according to a report by one of the world's biggest banks.
Analysts from Citigroup described independence as a "low probability, high risk event" in a report aimed at investors.
They said independence "looks even less likely now than a few months ago" but warned the possible consequences appeared "even more likely" to hit the economy, as uncertainty dissuaded firms from investing.
The report said the Scottish Government "seems to be pursuing a policy of sterlingisation" after Alex Salmond - whose favoured option of a formal currency union with the UK has been ruled out by the main Westminster parties - said Scotland could keep the pound without agreement.
The Citigroup report said the arrangement, which would leave Scotland without a central bank, would have "considerable disadvantages" for the country's financial services industry.
It added: "In our view it is astonishing that the Scottish Government, in seeking independence, has reached this stage without a clear plan for an issue as basic as its currency and monetary set-up."
The report came as Douglas Flint, the chairman of the UK's largest bank, HSBC, warned uncertainty over the currency of an independent Scotland could lead to "capital flight," as savers and investors shifted money elsewhere.
This would leave the country's financial system "in a parlous state", he said.
The pro-independence campaign group Business for Scotland blamed the UK Government for causing uncertainty by publicly ruling out the SNP's plan to share the pound in a currency union.
The group's chief executive, Gordon MacIntyre-Kemp, said: "Market pressure on the UK Government continues to build.
"The direct cause of any uncertainty real or imagined is the unsustainable and unprofessional stance of the No campaign and UK Government on currency."
He added: "It is in the best interests of the UK and a newly independent Scotland to negotiate in good faith towards a swift and mutually beneficial agreement on currency and debt following a Yes vote."
Earlier this week Crawford Beveridge, the chairman of the expert panel which developed the currency union plan, admitted the UK might turn its back on a deal if "politics trumps the economics" in negotiations following a Yes vote.
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