The difficulty for the 'No' campaign is one of 'credible threats'....it's simple game theory. The No campaign can say all it wants, but the reality is, if Scotland did vote Yes, they would have to negotiate, and there would be no incentive for them to stick to what they're saying right now.

The US and Russia understood this well - mutually assured destruction...the only way to make a threat credible is if it's impossible to back down.