ASDA warned prices could go up after independence, as 100 Scottish bosses yesterday threw their weight behind Better Together.
That came as finance and other retailers issued warnings of big changes if Scotland votes Yes.
A string of banks said they may have to move their legal HQs to London if Scots reject the Union.
Asda chief executive Andy Clarke said they would have to “reflect their cost” to operate their 61 stores and depots north of the Border after a Yes vote. Asda employ 22,000 people in Scotland.
Clarke said: “Our systems are set up for one single UK market, the same currency and the same rates of VAT. We achieve efficiencies and economies of scale.
“If we were no longer to operate in one state with one market and one set of rules … we would have to reflect our cost to operate here.”
Next and John Lewis warned shoppers may face higher prices and Sainsbury’s said they had already scaled back investment in Scotland because of uncertainty.
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BBC economics editor Robert Peston said the retailers’ bosses spoke out after one-to-one chats with David Cameron.
The IMF said independence would spook money markets and 100 Scottish business leaders – including travel tycoon John Boyle – backed a No vote.
Boyle said: “There are demonstrably no economic benefits and the demise of the Union could see us struggle as we lose all the benefit of this unique relationship blended over hundreds of years.”
RBS and Lloyds Banking Group, who run the bailed-out HBOS, said they had contingency plans to register their
businesses in England. At his international press conference in Edinburgh, Alex Salmond played down the threat as “brass plates” moving addresses.
But Better Together chief Alistair Darling said: “The only brass plate is the one that’s been nailed to the coffin of the economic case for separation by Scotland’s largest employers in the last 48 hours.”
RBS chief Ross McEwen made the bank’s position clear in a letter to staff yesterday morning, hours after rumours circulated.
McEwen said there would be no impact on customers across the British Isles.
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He added: “Our current business in Scotland is here because of the skills and knowledge of our people, and the sound business environment. So far, I see no reason why this would change should we implement our contingency plans.”
Clydesdale Bank said they would shift their registered address from Glasgow to England but there would be “no impact on the vast majority of the bank’s staff”.
TSB and Tesco Bank would also set up registered companies down south.
IMF deputy spokesman William Murray said there would be uncertainty about different monetary, financial and fiscal frameworks in an independent Scotland.
He added: “While this uncertainty could lead to negative market reactions in the short term, longer-term effects would depend on the decisions in the transition.”
Ex-RBS chairman Sir George Mathewson, who backs independence, said: “UK Government-driven scaremongering and political gamesmanship is of detriment to market confidence and the quality of democratic debate.”