WE were promised a "new phase" of the referendum debate at the start of the week.

And that's what we got – though not quite in the way we expected. The UK's legal advice on the constitutional status of an independent Scotland was supposed to demolish SNP claims that leaving Britain would be a smooth, seamless and speedy process. But that widely-spun notion was undermined when the co-author of the advice, the eminent Cambridge lawyer James Crawford, took to the airwaves to agree that the Scottish Government's 18-month transition timetable was realistic.

Meanwhile the macro-economic framework for an independent Scotland, published by Alex Salmond's most senior economic advisers on the same day, depicted not an oil-rich nirvana but a state facing the same financial pressures and need for austerity as the rest of the UK. The First Minister's oft-championed oil fund, it noted, was good "in principle" but in the near term cash generated from the North Sea would be required to pay for existing public services and reduce borrowing.

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Reassuringly, perhaps, the experts brought in by both sides proved rather more measured than their political sponsors. What the UK Government's legal advice and the Scottish Government's economic framework both emphasised was the importance of the negotiations that would follow in the event a Yes vote and it's here that the debate is heading in an unexpected direction. Gone, more or less, is the old game of claim and counter-claim in which implausible assertions by the Nationalist side were met with equally implausible scare-stories by their opponents.

There are some intriguing political implications.

From the SNP's point of view it keeps the debate on the process rather than the substance of independence, the "how" rather than the "what" or "why", for the time being at least. As with its recent transition timetable, culminating in independence day in March 2016, the focus on post-referendum negotiations helps create a sense that it is on course and a Yes vote is achievable – vitally important as yet another poll this week showed the Yes campaign trailing by more than 20 percentage points. However, it also poses a problem by introducing a large degree of uncertainty to the SNP's plans.

The pro-Union side will waste no opportunity to warn voters that a Yes vote represents a leap in the dark. What's more, they'll say it's a risk merely to re-invent the wheel. Labour refused to pour scorn on Mr Salmond's fiscal commission this week; it merely said its main conclusion, that Scotland should keep the pound, was a good argument for staying in the UK.

Referendum Minister Nicola Sturgeon hasn't yet quite found the language to frame the shifting debate. In her Government website blog she dismissed the UK's legal advice (which concluded an independent Scotland would be a new country, needing to negotiate membership of the EU and other international bodies) as "an act of breathtaking arrogance" and claimed the Government was displaying "a near colonial attitude to Scotland's position as a nation". But a couple of paragraphs later she relied on the argument that Scotland's future would be secured through "sensible and mature negotiation" conducted in a spirit of mutual co-operation and shared interest. Mmm. How many of you are now thinking: "With those arrogant colonial overlords? Really?"

Relatively little has been said so far about the nature of post-referendum talks or the Scottish Government's capacity to strike a fair independence deal. Or, indeed, the whole issue of what might constitute a fair, or good, or acceptable or poor deal on a myriad issues from rules on borrowing within the SNP's proposed sterling zone to provision of benefits. But without pre-negotiations, which have been ruled out by all sides, such questions will not go away before we go to the polls.