Standard Life, the Edinburgh-based financial services group, yesterday became the largest and most influential Scottish firm yet to warn about the possible impact of independence and said it was setting up English subsidiary companies in case it decided to relocate.
Unionist politicians said the actions of the Edinburgh-based firm showed leaving the UK would be a disaster for Scottish jobs. But, during ill-tempered exchanges in the Scottish parliament, first minister Alex Salmond insisted: "It is the case that not only will Scotland be a good place to do business, but it will be a more a competitive place to do business."
Royal Bank of Scotland also raised concerns about the prospect of an independent Scotland, saying it could hit the bank's credit rating.
Gerry Grimstone, the Standard Life chairman, said the firm, which employs 5,000 people in Scotland, was very proud of its 189-year heritage, but added "that if anything were to threaten this, we will take whatever action we consider necessary - including transferring parts of our operations from Scotland".
The mortgages to pensions firm, with pounds 237bn under management, highlighted uncertainties over an independent Scotland's currency, the shape of its monetary system, financial services regulation and taxes.
It also raised questions about whether an independent Scotland would be able to join the European Union by the Scottish government's preferred March 2016 target date.
The international ratings agency Standard and Poor's yesterday delivered its assessment of Scotland's financial standing as an independent country, suggesting it faces "significant, but not unsurpassable" challenges.
RBS further focused attention on George Osborne's decision to veto Salmond's proposals for a formal currency union, even though the bank's chief executive, Ross McEwan, was neutral about the referendum in public as he disclosed the bank's pounds 8.2bn losses last year.
Buried in its latest financial results, RBS said a yes vote on 18 September "would be likely to significantly impact the group's credit ratings and could also impact the fiscal, monetary, legal and regulatory landscape to which the group is subject".
In a detailed paper which will be closely studied by the City and overseas investors, Standard and Poor's (S&P) said Scotland had a "rich and relatively diversified" economy, broadly comparable to the UK's and Germany's in terms of its GDP, but would suffer growing pains with independence.
Salmond insisted that Standard Life's statements made an even stronger case for a formal deal to share sterling after a yes vote, to protect jobs and investments, and to set up shared banking regulation with the UK.
The excellence of Standard Life's 5,000 staff, who are chiefly based in Edinburgh, were a prime asset for the firm, he added. "My submission would be that Standard Life would find Scotland a good place to do business, as it does in 10 countries around the world."
Accusing the first minister of "denial, deception and delusion", Johann Lamont, the Scottish Labour leader, told MSPs that the transfer of so many jobs outside Scotland would exceed the infamous job losses under previous Tory governments when Ravenscraig steel works, a British Leyland plant at Bathgate and the former Peugeot Talbot factory at Linwood closed.
"If Scotland leaves the United Kingdom, people's jobs will leave Scotland," she said.
John Swinney, the Scottish finance secretary, said that City institutions and UK ministers would face a significant political and moral challenge to change tack on currency and banking union if Scotland's voters backed independence in September.
Pointing out that Standard Life had issued and then retracted threats to leave Scotland before devolution in the 1990s, Swinney said: "If the people of Scotland exercise their democratic right to vote yes in the referendum, it is incumbent on the UK government to respect the terms of the Edinburgh agreement [to hold the independence vote]."
Nicola Sturgeon, Scotland's deputy first minister, said S&Ps assessment supported her government's argument that Scotland was wealthy - the credit rating agency said that even excluding North Sea output Scotland was comparable to the UK's and Germany's triple A rated economies. "That is a glowing assessment of the Scottish economy from an impartial source and completely demolishes the scaremongering of the no campaign."
But Danny Alexander, chief secretary to the Treasury, said Standard Life's warnings underline "the concerns felt by many successful Scotland-based firms". He said: "It's commonsense that when you have something that works there will be adverse consequences if you rip it apart."
It is understood that the chancellors's statement in Edinburgh earlier this month vetoing a sterling zone and banking union was timed partly because the Treasury knew firms were anxious about independence and were preparing to announce their financial results to the City.
Standard Life is concerned at the prospect of an independent Scottish currency