There has been much discussion about the negotiating position the Scottish Government might take in the event of a Yes vote in the independence referendum but a new report from the Centre for Public Policy for Regions underlines both the superficial attractions and the hidden dangers in playing hardball.

It highlights the risks for the Scottish Government of making stroppy threats not to pay its share of debt if the UK Government would not agree to a currency union. The report confirms that, while paying a low or zero share of UK debt could indeed save the Scottish Government buckets of cash (equal in 2016-17 to twice that year's North Sea oil tax take), that benefit would have to be balanced against the fact that Scotland could face punitive borrowing costs on the international markets if it were seen not to have met its obligations following a bad-tempered dispute with Westminster.

Ultimately, that could be damaging to the Scottish economy. The report concludes that the stand-off is flawed and, unhelpfully for the SNP, suggests that negotiations over the removal of Trident is one area where a trade-off over debt levels might be reached.

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The report is useful in cutting through the bluster and gauntlet-throwing from both sides over what they would or would not be prepared to negotiate. It is clear that in the event of a Yes vote, nothing on either side should be off the table. That scenario remains theoretical, of course, and the pro-UK parties were out in force yesterday campaigning on defence. The Defence Secretary Philip Hammond stressed that the UK's armed forces, comprising Scots, English, Welsh and Northern Irish, epitomised the strength of the UK, while his shadow, Vernon Coaker, joined Alistair Darling and engineering boss Ian Walker in stressing the number of jobs in Scotland related to the UK defence industry.

But it was always going to be difficult for the main pro-UK parties to stand united and some antipathy was in evidence as Labour sources criticised the Defence Secretary for being too negative in his some of his remarks and for coming up to Scotland without consultation.

It should be obvious that the pro-UK parties cannot afford to be seen to bicker. Labour frustrations with the Conservatives are understandable, given that UK ministers have caused a string of problems for the No campaign by contradicting one another over whether or not the UK Government would negotiate about currency union or Trident and, no doubt, it was annoying for Labour to have Mr Hammond turn up without discussion. Even so, public division will not do their cause any good at all.

Yes Scotland has internal divisions too; for instance, the Scottish Greens and campaign chairman Dennis Canavan back a separate currency, not currency union as Alex Salmond favours. Because of the SNP's dominance in that campaign, it matters less.

An image of confidence and clear-sightedness will prove as important as arguments when it comes to winning this campaign.