The Edinburgh-based pensions, savings and investment giant - which employs 5000 people north of the Border - yesterday became the first major Scottish company to reveal it could quit. Whitehall says the Standard Life threat is the latest significant intervention to damage the Yes campaign since a pro-Union offensive began.
The Bank of England Governor Mark Carney warned on January 29 that a currency union would mean an independent Scotland ceding sovereignty to London. It was followed by a warning of "big uncertainties" around independence from BP chief executive Bob Dudley.
However, the UK Government believes the "dam" was breached two weeks ago when all three main UK parties made clear none would countenance the SNP's plan for a currency union. This led to Standard Life raising the prospect of relocating operations to England.
Meanwhile, the Royal Bank of Scotland warned a Yes vote could impact on its business. In a statement yesterday, the Edinburgh-headquartered bank said: "The group's borrowing costs and its access to the debt capital markets and other sources of liquidity depend significantly on its and the UK Government's credit ratings, which would be likely to be negatively impacted by political events such as an affirmative outcome of the referendum for the independence of Scotland."
But while Unionist politicians seized on the contingency plans being drawn up by Standard Life as a sign that independence would be a disaster for Scottish jobs, Alex Salmond sought to play down fears. He insisted Scotland would be a more competitive place to do business.
At First Minister's Questions, he said: "Standard Life will find Scotland a good place to do business as it, indeed, does business in 10 countries around the world."
Blair Jenkins, leader of Yes Scotland, said: "Standard Life wants a formal currency union and so do we. The only threat to that comes from the refusal of the No campaign and the UK Government to get involved in sensible discussions. We know common sense will win the day."
Danny Alexander, Chief Secretary to the Treasury, said: "What we've seen with Standard Life and RBS are the risks of independence becoming ever clearer.
"It's common sense that when you have something that works, there will be adverse consequences if you rip it apart. The strength and stability of the United Kingdom is the essential underpinning of Scotland's successful financial services sector over several centuries."
He added: "These businesses are reasonably and fairly setting out the consequences of the SNP's dangerous, risky and unclear plans for independence. I doubt they'll be the last."
The row broke after Standard Life's annual report revealed the firm, based in Scotland for 189 years, had begun to set up additional registered companies south of the Border to transfer part of its operations to "if it was necessary to do so". Some 90% of the UK customers of the Edinburgh-based pensions and savings company, are outwith Scotland.
Chief executive David Nish explained this had been done because of doubts over a "number of material issues" such as the currency and financial regulatory regime in an independent Scotland.
He said work to set up the companies was a "precautionary measure to ensure continuity of our businesses' competitive position and to protect the interests of our stakeholders".
It came on the day it emerged investments chief Keith Skeoch earned £4.2 million last year, the highest salary at the company. It compared with Mr Nish's £4.05m.
Business Secretary Vince Cable said Standard Life was "one of a series of Scottish finance companies giving warnings" while Alistair Darling, leader of the Better Together campaign, argued this was the reality of Scotland leaving the UK.
During exchanged at First Minister's Questions, Scottish Labour leader Johann Lamont said independence could damage the Scottish economy more than the policies of Margaret Thatcher.
In a reference to The Proclaimers hit Letter From America, she asked Mr Salmond: "Isn't it the case, if there is a Yes vote we'll have to rewrite the song - Standard Life no more, RBS no more, shipbuilding no more."
But the First Minister said there was "substantial evidence" that an independent Scotland would, in fact, be a more competitive place to do business.
He said the Scottish Government had put forward the "concept of a shared currency and regulatory framework" after independence, noting this was "exactly the sort of things Standard Life have been calling for".