Tuesday night’s televised independence debate revealed the depth of Alex Salmond’s biggest problem. The SNP leader believes too much that an independent Scotland would be self-evidently splendid. This leads him to assume that everyone who is against the concept is a fool or a coward. So his main tactic in his debate with Alistair Darling was to try to catch out a man who, in his eyes, is too cautious, too scared, too sensible. The slew of “But you said …” quotes from this newspaper and that, which Salmond used to try to make Darling look inconsistent, were too personal, all about undermining his opponent. It looked petty and trivial.

To win the debate, Salmond had to win over Darling. But he didn’t even try. Far from reassuring Darling that he was open to all kinds of ideas about currency, for example, Salmond stuck to his idea that Scotland will keep the pound, an idea that Darling was able to ridicule. I’d have liked Salmond to have asked Darling what his own Plan B would look like, if Scotland did vote yes. Darling would, after all, be on board, wouldn’t he, if that was what his country wanted from him? Instead Salmond just insisted that no Plan B would ever be needed, which anyone can see is terribly optimistic.

But the fact is that undecided voters are indeed cautious, unwilling to take the romantic leap of faith that Salmond made long ago. Undecided voters need reassurance, not for their worries to be sneered at or bulldozed aside. In reacting that way to Darling’s worries, Salmond did the same to those of the voters that he needs. Unless Salmond, in the next six weeks, can offer more than fingers-crossed bluster to those who fear the unknown, he’s not going to win any more hearts and minds than he has already bagged. He may even lose a few.

Above all, what Salmond needs to emphasise is that a yes vote on 18 September would simply be a signal, the start of a careful and civilised process, not some kind of sudden War of the Worlds in reverse, from which there would be “no going back”. It would be in the interests of the entire union to take the time to get that process right.

Perhaps it will take a long time to recast Scotland as a discrete member of the EU, for example. Fine. That’ll take the time it takes. There will be no great rush, no ticking clock. Moving Scotland’s centre of gravity from London to Edinburgh can be a leisurely and fascinating journey. It can be, as the phrase has it, a “conscious uncoupling”. We’d all still have to get along, and be able to trust and rely on each other, after all.

Darling argued that an independent Scotland would be a Scotland with a flag and capital but not a currency. Salmond missed his opportunity to remind us how much of the infrastructure of independence Scotland already has, how much it never saw fit to give up in 300 years. I guess he steers clear of that because the “no, thanks” folk can then ask what the point of full independence would be. Which is strange, because in the end there’s only one point: full democracy. And that’s the ground that Salmond is most sure on. Because why wouldn’t Scotland want that? And why wouldn’t the rest of the union want Scotland to have it?

For many on the left in England, the union’s main virtue is that it shields England from its own democratic deficits. In London, we can all prate on about the “two main parties” without seeing Salmond’s joke that there are more pandas in Scotland than Tory MPs as anything other than tired – which, of course, it is. But the fact remains: Scotland is done with the Conservatives, yet the Scots don’t have the power to ensure that the Conservatives are done with Scotland. They’re one of Britain’s, and therefore Scotland’s, “main parties”, and would remain so even if they had not a single Scottish seat at Westminster. It’s absurd.

What’s irksome about the unionist left in Westminster is that it thinks of Scotland as little more than a reliable chorus that can be counted on to swell the ranks. But a politically and fiscally independent Scotland could well contribute a great deal more than that to the cause of social democracy in England. This is precisely where Salmond’s leap of faith comes in. He believes that the Conservatives would stay rejected in Scotland, and that Scotland would be free, in a wholly positive way, of the unedifying, close-hugging wrestling match that Westminster politics has become.

Why isn’t the English left interested in seeing what might come of that, what decisive new arguments it could gain from political freedom north of the border? It’s even possible that Scotland and England could become more politically similar, once each country was allowed fully to confront and understand its own political reality instead of bouncing interminably between Labour and the Tories.

The truth is that Scottish independence doesn’t have to be the end of anything. Britain will still exist, and Scotland will still be part of it – it’s an island. The Commonwealth will still exist, and Scotland will still be a part of it – more’s the pity, some might say.

And, actually, the UK could still exist too, in some form, if the will existed to reshape it. That’s what Salmond is intimating when he talks of a currency union. It would be a paradoxical consequence of Scottish political independence if a Bank of the United Kingdom were finally to emerge from it. In fact, you could ask yourself why, if the union is so precious and important, we have muddled along without one for all these centuries.

Twitter: @DeborahJaneOrr