The Yes campaign surprised itself last week.

Though they would never admit it, many supporters had settled into a defeatist rut, consoling themselves that they had run the best campaign but in the end could not break through the default unionism of the "mainstream media" and its promotion of Project Fear.

Well, that's all changed. A Yes victory is now absolutely possible and we really could be living in the early days of that better nation. The only question is whether this extraordinary grass-roots campaign - the first truly "bottom up" political movement I have had the privilege to witness - really has the will to win, to press home its advantage.

What made the difference? Well, clearly Alex Salmond's victory in the second televised debate with Alistair Darling on Monday was a defining moment. It was not just that the First Minister found his form - actually he was still only firing on three cylinders, as anyone who knows him can testify. What really swung the event was the disintegration of the Better Together prospectus. We had always said that Alistair Darling was a one-trick pony, the trick being the currency, but no-one expected this to be so visibly exposed.

You'd have thought that, after his incoherence last time over what new powers would be granted to Holyrood, Darling would have come equipped with a glittering array of devo max offerings. Yet when Salmond asked him to name three job creation policies that would be devolved, he could only mention the Work Programme. Now, Scots have already been subject to this policy for three years and it has been widely condemned by everyone from the STUC to the Scottish Council for Voluntary Organisations for forcing young people on benefits to do unpaid work in places like Poundland. If this is the best advert for the Union, then God help the UK.

By equating the continuing union with workfare, Darling offered Scots a "Gradgrind Union" in which bankers call the shots and young people are exploited. It was a vivid illustration of his failure to offer any positive vision of what a continuing United Kingdom would look like; or why Scots should want to be part of it.

Politics is always about moral choices - especially in Scotland, where the communitarian electorate has always rejected crude appeals to self-interest. Scots refused to back the SNP's crassly materialistic "It's Scotland's Oil" campaign in the 1970s, just as they later rejected "loadsamoney" Thatcherism in the 1980s.

The Yes campaign was in danger of proving this a third time by putting up billboards all over Scotland asking Scots if they wanted to be rich. But you don't get to the hearts of the Scottish voter by appealing to their pockets, any more than you win their respect by resorting to threats.

New Testament morality is alive and well in Scotland, even though few Scots still go to church. They are more likely to throw the money-changers out of the temple than be told how to vote by them. Salmond understands this, so he turned the monetary tables by asking Darling if he would back the "sovereign will" of the Scottish people after a Yes and argue for the common currency that he had once agreed was "logical and desirable". This forced Darling to chose between Scottish civil society and the City of London, and he fell scowling into the trap.

Of course, he would not back the mandate of the Scottish people. The whole point of the currency diktat is to frighten voters, not look for a sensible solution to maintaining trade between Scotland and England. That morning, before a sell-out audience at the Edinburgh Book Festival, the Nobel Prize-winning American economist Professor Joseph Stiglitz had condemned that currency diktat as "a bluff". In Kelvingrove, it was finally called.

The pound has now largely been neutralised, I believe, as a campaigning issue, much as Europe has been. Of course, the press and businesses will still bang on about risks and uncertainties. But ordinary voters could never get terribly worked up about whose head is on the money they see less and less of in their pay packets. Like European Union membership, currency was always essentially an elite issue - of concern to unionist businessmen, Tories and Edinburgh bankers. What really motivates Scottish voters is fairness, jobs and the defence of the National Health Service.

Until last week, the Yes Campaign had observed a self-denying ordnance on the NHS, not wanting to be accused of resorting to Project Fear. Many had persuaded themselves that, since the NHS was devolved, it was intellectually dishonest to claim that it was at risk of being privatised. The Kelvingrove audience members demonstrated that on the contrary this is a now key referendum issue.

Many Scottish voters remain close to trade unions such as Unison - the largest health union - which has been telling its members that while the Scottish Parliament has operational control over the NHS, it does not control its financing. If the service in England is being privatised, as even Labour now accepts, it stands to reason that spending on it will eventually fall, and that this will be reflected in the Barnett formula.

By backing the bankers on the currency, and appearing to acquiesce in the privatisation of the NHS, Darling elected to place himself, as Salmond put it, "in bed with the Tories". That is a very dangerous place to be for any Scottish politician.

Every Scottish voter knows that Scottish business is in bed with the Tories. This was confirmed by David Cameron's latest day trip to Scotland where he elected to speak not to the people of Scotland, but to the bosses' "union", the CBI.

It is becoming clear that Cameron's refusal to debate with Salmond has been a major error for Better Together. It makes the Prime Minister look like a pusillanimous absentee landlord. Scots would have respected him for coming to debate with the First Minister. And I genuinely believe Cameron would have made a better case for the Union than Alistair Darling. At least Cameron has been able to say that Scotland could be "a successful independent country". Alistair Darling has been incapable of uttering those words, which seem to cause him almost physical pain. The message from him is clear: Scots should accept their place, and not get ideas above their station.

This patronising attitude to the voters was summed up by The Woman Who Made Up Her Mind, Better Together's recent campaign TV broadcast. This was supposed to be couthy and populist, but it aroused genuine anger among many women voters.

The broadcast put the tin hat on a disastrous week for the unionists. It would have been much worse still had the Yes campaign been able to seize the initiative with the press after Monday's debate.

Better Together still runs a superior media campaign, even if it lacks colour and popular engagement. It has a grid, if nothing else, and works closely with its friends in the press to ensure the negative messages hit home - which explains why the days after the debate were dominated not by Darling's performance but by a letter from unionist businessmen and then a speech from the football commentator, Archie Macpherson.

Yes should have been more proactive, perhaps sending a Jarrow March of young people on the Work Programme to pursue Darling; issuing an open letter from NHS consultants; getting the BMJ to condemn Coalition health reforms as "madness". As Labour discovered in the early 1990s when it faced a similar media lock-out, there is no point complaining, you just have to come up with stories that force alternative views onto the agenda. This requires close personal contact with journalists in unsympathetic newspapers.

The Yes campaign is brilliant on the ground, in public meetings, on social media. But it still needs to get across to those voters whose attitudes are still formed by what they read and see on television.

But be in no doubt: after this momentous week, victory is within the Yes campaign's grasp. We may be about to witness, in little more than two weeks, the greatest earthquake in British constitutional history.