PM steps up the rhetoric ahead of Salmond talks

David Cameron will today raise the rhetoric of the debate over Scotland's future by describing the UK as "precious" and promising to fight "head, heart and soul" to keep the union intact.

In what will be seen as a major rallying call from London to defend the union, the Prime Minister will claim the issue of Scotland's potential secession has now gone beyond basic "policy, strategy or calculation" and for the first time will admit "our shared home is under threat".

In the speech in Edinburgh ahead of talks with Scotland's First Minister, Alex Salmond, Mr Cameron's focus will be on what he calls the "entirely positive" and "practical" aspects of the union. If the Treasury and the Chancellor, George Osborne, preferred Downing Street to travel to Edinburgh armed with numbers rather than emotions, they will be disappointed.

Although admitting there were arguments over oil, debt and the UK's banking system, Mr Cameron will insist that Scotland "just as much as England, Wales and Northern Ireland" is "stronger, safer, richer and fairer" inside the UK.

The speech will also be No 10's first direct response to the Scottish Government's almost unilateral declaration earlier this week that both Holyrood and Westminster had "more or less" settled on autumn 2014 as the agreed date for a referendum.

If Mr Cameron again questions the 2014 date, and repeats his preference for a "sooner rather than later" poll date next year, he opens up the prospect of Mr Salmond attacking Westminster for going back on an issue he believed had been settled.

However, before the face-to-face talks with the First Minister, Mr Cameron will point to the UK's permanent seat on the UN Security Council, clout inside Nato and Britain's "unique influence" in global politics as institutional assets that could be lost to an independent Scotland.

He will also claim that the UK's defence capabilities, running the world's fourth largest defence budget, would be lost to Scotland's five million population if they chose to leave.

Last night at a speech at the London School of Economics, Mr Salmond said the economic case for Scottish independence was "absolutely clear".