(Reuters) - BlackRock Inc (BLK.N), the world's largest money manager, warned that Scottish independence would bring about "major uncertainties, costs and risks" in Britain, becoming the latest company to join the debate on this year's referendum.
Scotland will vote on whether to end its 307-year union with England in September.
The British government has been campaigning fiercely to keep it intact, arguing that both countries are better off together, while Scotland's nationalists believe a split would give them the economic freedom to prosper.
"(A 'Yes' vote) would create risks for investors, corporations, savers and the UK economy," BlackRock said in a detailed report for professional clients, adding that investors in gilts, banks, utilities and energy companies would be most affected.
It said there could be limited pressure on gilt prices due to the small probability of Scotland finding it difficult to meet its obligations to England at some point in the future.
But weighing out the potential impact of independence on gilts in four scenarios, BlackRock concluded that there would be no material risk for Britain's debtholders unless Scotland defaulted on its share of the liability.
BlackRock said independence would raise regulatory costs for banks and insurers that would move employees to England to avoid having to pay additional fees to a new Scottish regulator.
Major banks would also question whether or not Royal Bank of Scotland (RBS.L) should remain based in Scotland, BlackRock said, as Britain's support to the bank since 2008 has totaled more than 210 percent of Scotland's gross domestic product.
The New York-based investment manager highlighted the impact of other major issues that had to be settled, including Scotland's opening balance sheet, the division of its hydrocarbon bounty, European Union membership, tax matters, and choosing a currency.
Weighing the costs and benefits of Scotland's three currency options, BlackRock ranked Scotland launching its own currency above keeping the British pound or joining the euro.
BlackRock, which manages more than $4 trillion in assets, said it expected Scotland's initial credit rating to possibly be several notches below Britain's.
It added that credit investors would factor the uncertainty of "volatile" North Sea oil revenue into yields and that it was "probably unwise" to base fiscal spending on crudes that depend so critically on energy prices, production volumes, costs and tax incentives.
"The current Scottish Government will be hard-pressed to deliver many of its promised outcomes," the investment manager said, adding that negotiations would likely drag beyond the 2016 timetable.
BlackRock's concerns follow a string of warnings from fellow financial services companies including RBS, Standard Life SL.L and Barclays (BARC.L). The bosses of oil majors BP (BP.L) and Royal Dutch Shell (RDSa.L) have also voiced arguments against Scottish independence.
A poll published on Sunday showed that the number of Scots ready to vote for independence rose to 39 percent, up 2 percentage points from a similar survey conducted last month. The data added to evidence that the referendum on September 18 could be tighter than previously expected.
Reporting by Richa Naidu in Bangalore and Simon Jessop. Additional reporting by William James in London; Editing by Bernard Orr