This then assumes that a Scotland with new economic powers would not want to take responsibility for either bank.
Indeed, the proposal is for a new Scottish bank to manage Scottish borrowing and Scottish lending.
Leave aside the costs of establishing the banks - 1,000 branches, 20,000 staff, a new computer system and meeting the lending leverage requirements of Basel 2 - and let's focus on the immediate position.
The two big Scottish banks will be under the control of a foreign Government with a potentially different economic agenda.
Ireland grew, burnt and crashed because it's low-tax economic policies couldn't be reflected in its fiscal controls to revalue the exchange rate or to reduce interest rates. Greece, at the other end of the spectrum, had exactly the opposite needs, and it too has burnt and crashed. The economic power house that is Germany has set the economic framework to benefit Germany - and France until this weekend.
Scotland applies Plan MacB whilst the UK carries on as is: so the RBS and BoS follow a different economic policy and Scotland is strangled. Or if the UK has got it right and Scotland has it wrong, the banks flood the economy with cheap money and cause rampant local inflation and the collapse of business.
Something like 60% of the retail banking sector would be owned by a foreign Government (with a grudge), and 99.9% of all banking capacity will be controlled from outside the country for at least 5 years.
Good move? I think not.