A "new phase" in the Scottish independence poll campaign gets underway on Monday when the UK Government publishes the first in a series of analytical papers, which it hopes will help convince Scots to vote to keep Scotland within the UK.
The first paper, pulled together by ministers and civil servants from several UK Government departments and drawing on the views of constitutional and legal experts, will set the general context to the debate with a document that lays out the legal basis and history of the UK and Scotland's place within it. It will make reference to treaties and institutions, including the EU.
Earlier this week, Deputy Prime Minister Nick Clegg said it would provide hard facts as well as "objective, dispassionate analysis" and would set out "claims and counterclaims in objective detail".
One Whitehall source described the analysis paper as "a serious piece of work, which will mark a new phase in the referendum campaign" while another insisted it would be "far more substantial than the incredible stuff put out by the SNP Government".
On Tuesday, the Scottish Government outlined in a 16-page document its transition plan to independence should Scots vote yes.
It said the process would take just 17 months, with First Minister Alex Salmond announcing that independence day would be in March 2016.
However, pro-UK leaders denounced the plan as "fanciful".
Lord Falconer, the former Labour Lord Chancellor, said the timescale was impossible, noting: "They are going to separate the English and Scottish armies, they are going to negotiate 14,000 international treaties, they're going to set up a supreme court and join Nato as well as negotiate in relation to the EU. I don't know what the civil servants and politicians are going to be doing except for that."
The first paper on the legal basis of Scotland within the UK has been co-ordinated by the Cabinet Office and will look at the practical differences between devolution and independence and what "secession from the UK" will precisely mean.
This weekend, David Cameron is expected to use the launch of the first part of what has been dubbed the "manifesto for the UK" to underline his personal commitment to the Union.
Whitehall sources say this issue is clearly the PM's top priority as the full intellectual might of UK Government departments is being deployed.
The Treasury is spearheading the co-ordinated push with Sir Nicholas MacPherson, the department's top civil servant, chairing a group of permanent secretaries.