THE International Monetary Fund has warned uncertainty over an independent Scotland's currency would spook the financial markets in the immediate aftermath of a Yes vote.

The warning came as five banks confirmed plans to register their headquarters south of the Border if Scotland leaves the UK.

In a separate development, Bank of England Government Mark Carney issued figures showing an independent Scotland would face tax rises or spending cuts of £21 billion, equivalent to £4000 per head, if it kept the pound without a formal currency union with the UK, as the country built up cash reserves.

The No campaign seized on the announcements, claiming they showed Alex Salmond's plans would cost jobs and drive down living standards.

However, the Nationalists welcomed interventions by two of Scotland's leading financiers.

Martin Gilbert, head of investment house Aberdeen Asset Management, said the country could prosper regardless of the outcome of the referendum next week. He also insisted the Scottish Government's preferred option of a formal currency union between an independent Scotland and the rest of the UK would be "highly likely", despite it being repeatedly ruled out by the three main pro-union parties.

Sir Angus Grossart, chairman of merchant bank Noble Grossart and one of the most influential figures in the Scottish financial establishment, said warnings about the market's reaction to independence had been "severely overstated".

Urging people to "stay cool and not panic" he added: "I think it is getting out of hand, a severe overreaction … to hear some of the comments you almost expect people to be predicting a plague of locusts or mice next."

The IMF, the body set up to ensure financial stability around the world, said a Yes vote would create "uncertainty" in the short term over Scotland's currency arrangements.

"While this uncertainty could lead to negative market reactions in the short-term, longer-term effects would depend on the decisions being made during the transition," a spokesman said.

Earlier in the day Royal Bank of Scotland, based in Edinburgh since 1727, and Lloyds Banking Group, which includes HBOS, confirmed plans to move headquarters south in the event of a Yes vote. Australian-owned Clydesdale Bank also said its contingency plans for a Yes vote included re-registering as an English company to mitigate risks and provide increased certainty for customers.

Edinburgh-based TSB said it would establish additional legal entities in England in the event of a Yes vote, while Tesco Bank said it would redomicile in England.

RBS said the move would not affect jobs or operations and LLoyds stressed its plans were a "legal procedure".

Chief Secretary to the Treasury Danny Alexander said: "The news today that all of Scotland's major banks are putting in place contingency plans to relocate their HQ functions is of the utmost seriousness for Scotland. In the short term, jobs and tax revenues would be lost.

"But in the longer term, the centre of gravity and decision-making of Scotland's financial sector would have shifted to a foreign country."

But former Royal Bank chairman Sir George Mathewson said: "There is no real jobs, revenues or investment impact in any of these technical announcements.

"They are also very similar to what has been said before.

"In any event, of course there will be a currency union in the interests of both Scotland and the rest of the UK.

"The UK Government-driven scaremongering and its political gamesmanship is of detriment to both market confidence and the quality of democratic debate.

"Voters will not be swayed by these tactics."

Welcoming the comments by Mr Gilbert and Sir Angus, Scottish Finance Secretary John Swinney said: "As Martin Gilbert says, an independent Scotland can and will be a big success. With the powers of independence we can support our economy and ensure continued economic growth."