TENSE doesn't describe it.

On Monday afternoon, the Prime Minister might have been outwardly engaging with MPs on threats from foreign lands when he gave his Nato statement, but inwardly his focus was nearer to home and the threat to the United Kingdom - and possibly his own premiership - from the separatist cause in Scotland.

Shortly after 5pm, Mr Cameron and his top advisers quickly withdrew to his oak-panelled Commons office, where minutes later Ed Miliband and his senior aides trundled in. What to do about Scotland?

Last week, as the PM left the Nato summit in Wales a rumour began to circulate that a weekend poll could see the No lead dramatically narrow further. Of course, it turned out that in one snapshot, it disappeared completely and placed the Yes camp's nose in front.

Coalition insiders insisted there was "no panic just nervousness" that, while there was an expectation the polls would narrow as September 18 approached, a lead for Alex Salmond and his cohorts, however slim, had the potential to result in defeat being snatched from the jaws of victory. To Coalition outsiders, of course, the UK Government's manoeuvrings did indeed smack of panic.

One senior Whitehall source declined to say whose idea it was to have a combined sortie north but that "in the circumstances it was felt they would do far more good in Scotland promoting the Union than trying to score political points from each other at Westminster".

Another added: "The PM is determined to keep the message going right to the end."

Just as the London media have belatedly woken up to the independence story and are now serial questioners on the subject at No 10 briefings, so too it seems referendum fever has suddenly caught English MPs' imaginations.

There is a strange detached feeling at Westminster as MPs gather in the Commons bars, restaurants and cafes to talk Scotland. Like relatives sitting by a loved one's hospital bed, hoping for the best but not really being able to do anything, most MPs, particularly Tories, feel somewhat helpless at being able to save the Union.

One former minister rolled his eyes at how Mr Cameron had handled the Scottish question. "Terrible. Cameron, Osborne? They're children. There's no strategy, they're just reacting to things tactically. It's a total nightmare."

Bernard Jenkin, a wily, seasoned Conservative, is deeply concerned that Scotland could, after 300 years, break loose.

"Many people at Westminster are waking up to the nightmare of a Yes vote and are therefore hoping that Scotland will remain in the UK. A break-up would be a political earthquake beyond our imagination. I'm sure the Scottish people will draw back from the abyss," said the Essex MP optimistically.

Yet, there are some English and Welsh Conservative MPs who believe there is a political opportunity to be had from a Yes vote across the Border.

One Tory backbencher claimed he and many of his colleagues were "not emotionally involved" and really "did not care" about whether Scotland stayed within the UK.

But a more senior Conservative was aghast by some of his colleagues' "we must speak for England" sentiment.

"Most people are principled and Unionists but there is a certain type of Conservative MP who says if there is independence, there will be 40 fewer Labour MPs and there is more chance of a Tory government; we must speak for England. It breaks my heart."

While Mr Miliband has insisted all his Shadow Cabinet and at least 100 Labour MPs venture north between now and polling day, the Tories appear to be staying largely put south of the Border, hoping, in the main, that the Union patient, whose hand they are holding tightly, pulls through.

From Westminster, as elsewhere, it now seems touch and go.