Scottish independence would spark "massive recriminations" in Westminster and increase the likelihood of Britain leaving the European Union, a French investment bank has warned.
Societe Generale economist Michala Marcussen warned that a vote by Scots to break away from the United Kingdom on Thursday could see the Tories challenge David Cameron's leadership.
"A Yes vote to Scottish independence would increase the risk of Brexit - a UK exit from the European Union - with a referendum then more likely to take place in 2017," Marcussen wrote in the bank's latest Global Economics note.
"Such an outcome would lower trend potential in both the UK and the euro area. Indeed, for both, the other is the largest trading partner."
This comes as a centre-right think tank warned that Scottish nationalists had severely underestimated the economic risks of independence.
The Centre for Policy Studies said in its report entitled "Why Scots Should Say No" that an independent Scotland would face three major risks in oil, finance and pensions.
The think tank, which was founded by former Tory prime minister Margaret Thatcher, suggested that there was a £13.8 billion "hole" in an independent Scotland's prospective budget. Its report warned that the North Sea revenue for the Scottish government would fall from £10.1 billion in 2011-12, but only £5.5bn in 2013-14, to £3.7bn in 2016-17, some £3.2 billion adrift of the £6.9 billion predicted by the Yes campaign.
The report also warned that the "probable" flight of a large section of Scotland's financial services sector, as indicated by the announcements from RBS, Lloyds, Clydesdale and Standard Life last week, could leave revenues of £47.7 billion in 2016-17, excluding North Sea oil, which is about £9.2 billion lower than the £57.3 billion forecast by nationalists.
"Together, omission of these three factors results in a severe understatement of independence risk, both to Scots in general and to public sector workers and retirees in particular," the report warned.
"The cumulative impact of these three risks on Scottish government revenues would be £13.8bn in 2015-16. Total government revenues could be £50.4bn, far below the 'yes' campaign's own estimate (£64.2bn) and far lower, too, than the £63.3bn that Scotland is expected to spend in that year."
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A Better Together spokesman said in response: "The risks of separation have become clearer every day. By not answering the fundamental questions and not being honest with the people of Scotland the nationalists are putting jobs, pensions and our NHS at risk.
"We can have what the majority of Scots want - more powers for Scotland without taking on all of the risks of independence. It's the best of both worlds. We should say No Thanks on Thursday."
A spokesman for Scottish Finance Secretary John Swinney said: "It is little surprise that a think tank co-founded by Margaret Thatcher is against an independent Scotland, and this report is stuffed full of basic factual errors.
"Scotland is among the top 20 wealthiest countries in the world, and we have a once in a lifetime opportunity on Thursday to vote Yes and ensure that Thatcherite policies can never again be inflicted on the people of Scotland from Westminster."