In the week of the Conservative party conference, the consequences of not getting out of the house early in the morning with a firm sense of purpose can be punitive. You find yourself aimlessly flicking through the news channels until, inevitably, you happen upon the Tories smiling rather dauntingly and, not for the first time, you expect there to be a commentary by David Attenborough: another world, another species.

The Tories are best encountered late at night in the company of a stiff whisky and Andrew Neil to make sense of them all. To begin the morning with an earful of privileged millionaires bashing the long-term unemployed, the young unemployed and the NHS can set a dispiriting tone for the rest of the day.

Yet during David Cameron's speech, you acknowledge once more that he was born for this and that every ounce of a privileged and confident education was coming together effortlessly in a walking, talking advert for Eton and Oxford. The prime minister is an excellent public speaker and possesses those clear and slightly high-pitched cadences of his tribe that are impossible to conceal and which announce their presence startlingly in quiet restaurants.

A live debate between him and Alex Salmond on the question of Scottish independence would be one of the political events of the century so far and would easily eclipse those rather queasy and stuttering leaders' debates in 2010 that, inexplicably, the glove-puppet Nick Clegg was deemed to have won.

Yet Mr Cameron has, thus far, been running scared of a public confrontation with Scotland's first minister. It is a curious position to adopt for a man who, only four months ago, had sworn to defend the union with "head, heart, body and soul". Right now, Mr Cameron is defending the union with his big toe.

The prime minister would prefer that Mr Salmond engage instead with Alistair Darling, leader of the Better Together campaign. He justifies his reticence thus: "You want the independence debate to be an argument between you and me; the Scottish government and UK government; the SNP and Conservative party – in fact anything rather than what it really is about. Nor is your argument with the rest of the United Kingdom – it is with the people in Scotland."

Mr Cameron couldn't be more wrong here and I fear he is listening too much to the No strategists in Scotland whose dire campaign so far has been to plant silly scare stories with their media chums and to throw the phrase "anti-English" around a lot.

First, any debate that includes Alistair Darling would risk sending the nation to sleep and having all future televised political debates cancelled for all time. And why should Scotland's twice-elected leader debate with a semi-retired Westminster backbencher? Second, it is absurd that the democratically elected leader of the United Kingdom wants to hide at the very point in history when the union he leads is under unprecedented mortal threat.

This may indeed principally be a debate among Scots, but it is also about the future of the UK. People living elsewhere in the UK may not be able to participate in the referendum but Mr Cameron has a moral duty to be their voice as the debate unfolds.

In Belfast in 1912, Winston Churchill was assailed by a loyalist mob before he delivered the following words about Ireland: "History and poetry, justice and good sense, alike demand that this race, gifted, virtuous and brave, which has lived so long and endured so much should not, in view of her passionate desire, be shut out of the family of nations and should not be lost forever among indiscriminate multitudes of men."

There wasn't then the clamour for a leadership debate on Ireland's future, but it is inconceivable that if the Scottish independence battle had fallen within his political career Churchill would have run away from the battle as Cameron is now doing. Churchill saw Britain as a global superpower built on its leadership of all the English-speaking peoples.

He wasn't against a united Ireland – so long as it remained part of the United Kingdom. Churchill would have brought his formidable powers of oratory to bear in this debate and would have traduced any aide who sought to advise him otherwise.

There is a lazy narrative surrounding the question of Mr Cameron's participation in a head-to-head encounter with Scotland's first minister. It says that Mr Salmond, a formidable debater, would simply trounce Britain's prime minister. This, though, bears little proper scrutiny either.

Certainly, Mr Salmond has been winnowing his argument for independence and trimming his delivery throughout his entire adult life. But Mr Cameron's declamatory skills are not inconsiderable and if he is as passionate about the union as he claims to be then he would be a worthy opponent for Mr Salmond.

The nationalists remain vulnerable on the nuts and bolts of pension provision, public expenditure from a low tax base and meeting Scotland's share of the UK debt. So it's not as if there isn't plenty for the prime minister to aim at.

It would also be an ideal opportunity to reveal what new devolved powers Scotland could obtain following a No vote (which would hand it the title of Most Independent Non-independent Country in the World).

The poll gap between Yes and No will shorten considerably in the run-up to the independence referendum. The 20,000 or so people who gathered in Edinburgh two weeks ago for the independence march and rally will all be campaigning avidly on doorsteps next September.

The No campaigners know that they simply couldn't muster that amount of people marching under the union flag outside of an Orange parade. When these numbers begin to tell it will be time for Mr Cameron to step up to the mark.

If he continues to hide, he risks being remembered as the leader on whose watch a quarter of the kingdom was lost and who barely raised a gallop in its defence. And if the leader of the United Kingdom cares so little about Scotland being part of it, then why should any of the rest of us?