That is why the pro-independence campaign would like to recreate a currency union in the event that Scotland separates from the rest of the UK.
"If there was a better alternative that improved the future prospects of Scotland it would surely have been promoted vigorously."
He added: "The alternatives to a currency union include a completely independent currency, passive acceptance of a monetary policy designed in London for the rest of the UK, or, assuming Scotland rejoins the European Union, eventual membership of the euro.
"In all these circumstances, the transition from the existing currency union would be complex and fraught with danger.
"At the extreme, uncertainty over Scotland's currency arrangements could prompt capital flight from the country, leaving its financial system in a parlous state."
HSBC is the second largest bank in the world but has a relatively small presence in Scotland, with 10 branches.
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