Grrr, I hate it when politician's show how really stupid they are. Especially when they are the finance secretary yet can't even get the basics right. The debt is not £125 billion. That's the UK annual deficit. The UK debt is over £1 trillion and mounting.
I've no clue if it is true that Scotland could walk away from their share. Certainly if I were the Scottish first minister I'd be tempted to try. Just in the same way a man in debt will always be tempted to use a loophole to wriggle out of paying.
I suspect the reason this hasn't been widely reported is because it probably is the opinion of a few people with particular agendas and not commonly accepted fact. In other words other equally 'qualified' people may well have totally opposite opinions. I don't know, just a hunch.
But to me the whole SNP bid for independence doesn't stack up. They want to quit the UK but then reapply to Europe. As a new tiny minnow state they'd have a small voice and happily ignored by the heavyweights like France & Germany. At least the UK has a veto for certain things. Scotland would have no such veto. All laws passed would be thrust down their throats.
As new members of the EU they'd be obliged to sign up to implement the Euro eventually. But that takes time so they want to keep the pound. Except the interest rates and all policy decisions would be made in England. Where of course now they have no influence.
And as net recipients of taxpayer money in the UK they'd have to rely heavily on North Sea oil to balance their books. But as we all know oil is a finite resource. So longer term for me that is a dangerous thing to do.