Speaking in Glasgow the Chancellor has said:
The SNP asserts that it would be in everyone's interests for an independent Scotland to keep the pound as part of a eurozone-style sterling zone.
But the Treasury analysis we are publishing today shows that is not the case. Let's stop speculating and look at the evidence.
– George Osborne, Chancellor
Would the rest of the UK family agree to take that risk? Could a situation where an independent Scotland and the rest of the UK share the pound and the bank of England be made to work? Frankly it's unlikely because there is real doubt to the answers of these questions.
In other words the only way to be sure of keeping the pound as Scotland's currency is to stay in the United Kingdom.