LONDON (Reuters) - Insurance and pensions heavyweight Standard Life (>> Standard Life Plc) became the first major company to warn it could move partly out of Scotland if Scots split from the United Kingdom, fuelling a political row over the financial impact of independence.

The company, which has been based in Scotland for 189 years, revealed on Thursday that it had a contingency plan to partly move from Scotland, potentially putting 5,000 jobs at risk.

In a double blow to nationalists, the Royal Bank of Scotland (>> Royal Bank of Scotland Group plc) also said a vote for independence would probably significantly hit its credit ratings, impacting its costs.

Their comments come as a dispute over currency has ignited the debate, with Scottish leader Alex Salmond wanting to share the pound in a currency union with the rest of the United Kingdom but the major British parties rejecting this plan.

"Standard Life and RBS's comments will have an impact on the debate as they are totemic institutions that represent a really important part of the Scottish economy," said Simon Clark, head of the school of economics at the University of Edinburgh.

Scotland is home to the second largest financial services industry in the United Kingdom, accounting for about 150,000 jobs.

The Scottish government said the comments backed its argument that a monetary union was best for businesses both sides of the border, calling for talks with the UK government.

But the UK government, represented by Treasury Chief Secretary Danny Alexander, said Standard Life and RBS's foray into the ring showed the risks of independence becoming clearer.

To date few businesses have publicly stated their plans for what they would do if Scotland voted on September 18 to become independent as the likelihood of a "Yes" vote had seemed remote.

SEPARATING BUSINESS FROM POLITICS

But with the nationalists starting to gain ground in the polls, with about 37 percent support compared to 47 percent opposition to independence, increasing numbers of business leaders have started to talk about possible financial risks while steering clear of the political bullring.

Standard Life said it was setting up registered companies in England "as a precautionary measure" into which it could transfer operations if Scots ended a 307-year tie to England to ensure its competitiveness and interests of its stakeholders.

Chief Executive David Nish said this was necessary due to uncertainty over how an independent Scotland would work, such as its currency and if it would join the European Union.

"We have started work to establish additional registered companies to operate outside Scotland into which we could transfer parts of our operations if it was necessary to do so," said Nish, stressing the company was politically neutral.

Standard Life manages more than 244 billion pounds of assets for its clients, around 90 percent of whom are outside Scotland.

RBS, once the world's largest bank with 12,000 staff in Scotland, said in the risk section of its annual results on Thursday that independence could impact its credit ratings and the fiscal, monetary, legal and regulatory landscape.

But Chief Executive Ross McEwan said the bank had yet to make plans for a "yes" vote, saying the company was neutral and "won't do anything to raise the temperature of that vote".

Ratings agency Standard & Poor's said an exodus of banks could create volatility for Scotland's liquidity and investment.

"On the other hand if this were to happen, it could bring benefits in terms of reducing the size of the Scottish economy's external balance sheet, normalising the size of its financial sector, and reducing contingent liabilities," it said.

"In short, the challenge for Scotland to go it alone would be significant, but not unsurpassable."

"RUNNING FOR COVER"

Ronnie Ludwig, a senior tax adviser in Edinburgh for financial advisory firm Saffery Champness, said Standard Life taking a public stand about a possible move to England was significant and could prompt others to follow suit.

"The lack of certainty over the pound, EU membership and the tax regime, be it corporate or personal, is driving a culture of, at worst, fear and some are starting to run for cover," Ludwig told Reuters.

A poll by executive search firm Korn Ferry released this week found 65 percent of chairmen of 32 FTSE 100 companies said it would be bad for business if Scotland became independent.

With the row over the pound taking centre stage, Salmond has accused the British parties of bluffing, arguing if there was a vote for independence they would enter negotiations as a shared currency was best for both sides. They are major trading partners who would want to avoid currency translation costs.

Scotland's Finance Secretary John Swinney maintained the insistence on Thursday that an independent Scotland would keep the pound, sidestepping call for details of a Plan B.

"Scotland has a strong and diverse economy and the point of independence is to win the powers we need to build on those strengths and create a more prosperous and secure economy which is good for the financial sector and everyone else," he said.

(Additional reporting by Jemima Kelly and David Milliken, Steve Slater, Editing by Angus MacSwan)

By Belinda Goldsmith and Chris Vellacott

Stocks treated in this article : BP plc, Standard Life Plc, Royal Bank of Scotland Group plc