It's a ruse by Salmond. He is goading the UK into saying "no" to a shared currency so that Scotland can't, by law, pick up a share of the national debt.
Instead what is likely to happen is that Sterling will be split into two: A British Pound and a Scottish Pound. Scotland will get its share of the Bank of England assets and the rest of the UK will get its share. Similarly the debt will be split so that Scotland takes their share of the debt and rest of UK takes its share. Currently the UK government is saying that it will back up all the debt to prevent the threat of independence causing a down rating of debt. It's highly likely that if independence goes ahead then they'll back track on that saying that the situation has changed and that borrowers will have their debt split between the two new nations. That or if Scotland say they don't want any of the debt then they won't get any of the assets either.