They think it's all over. The leaders of the unionist Better Together campaign are already congratulating themselves on victory in next year's referendum. Indeed, the US statistician and election forecaster, Nate Silver, told the Edinburgh book festival last week that the yes campaign had "virtually no chance" of winning. But unionist triumphalism may be premature.

At this stage in the 2011 Scottish parliamentary elections, the Scottish National party was more than 10 points behind in opinion polls, and pollsters gave it little chance of winning. Yet Alex Salmond went on to secure a landslide, delivering what most commentators – this one included – had said was impossible: an absolute majority of seats in a Scottish parliament elected on a form of proportional representation.

It has been a constant of Scottish politics for the last 20 years that only around a third of voters tell opinion polls that they want to leave the UK. The key to the referendum result lies in the majority – between 50% and 60% – who say they want a Scottish parliament with greatly enhanced economic powers. Supporters of what has been called "devolution max" or "devolution plus" have effectively been disenfranchised because there is no third option on the ballot paper.

The SNP first minister, Salmond, called for this third way to be included, but was rebuffed by Westminster. A significant proportion of undecideds could be persuaded to lend their votes to the yes campaign, not just because they have been denied the opportunity to vote for their preferred option, but because they fear the consequences of Scotland saying no.

Scotland has bitter memories of what happened after the abortive 1979 devolution referendum, when it narrowly voted yes to a Scottish assembly, but not by a sufficient margin to reach the 40% of the electorate required under the Scotland Act.

Scotland fell off the Westminster map in the 1980s, as Margaret Thatcher decided the Scottish question had been answered. A decade of industrial collapse and public spending cuts culminated in the hated poll tax being introduced in Scotland a year ahead of England. Meanwhile, around £100bn worth of oil revenues went south, returning only partially to Scotland in the form of unemployment and invalidity benefits.

Scots have little confidence in the vague promises made by the unionists today of "more powers" for Holyrood if Scotland votes no in 2014. This is precisely what Thatcher promised before 1979, but abandoned on the grounds that there was "no consensus" on what a better devolution should look like.

Meanwhile, Salmond is offering yes voters what he calls a "new UK", a "social union" – keeping the Queen, the pound, Nato and the Bank of England. This is different from the isolationist independence of old.

The unionist campaign has been patronising, cynical and relentlessly negative, based on scares that Scotland would be ejected from the EU, Nato and other international bodies. That Scots would be denied the pound, pensions and mobile phone tariffs if they voted yes. This is not the way to win hearts and minds.

But even if Scotland votes no, I believe it will eventually end up with a form of independence, though it may not be called that. The existing constitutional settlement already leaves most domestic legislation – education, health, criminal justice – with Holyrood, and the case for greater economic powers has largely been accepted, not least by the unionist-inspired Calman commission in 2009, which argued that to be accountable, a parliament must raise, in tax, the bulk of the revenue to pay for its spending policies. This must come – indeed, partial income tax-raising powers will be devolved next year under the recent Scotland Act.

Few in London would seriously lament the loss of Scotland, or the disintegration of an imperial entity – the UK – that no longer has an empire. In some opinion polls, more English voters support Scottish independence than Scots. Scotland is dominated by two parties of the traditional social democratic left: Scottish Labour and the Scottish National party. The standing joke is that there are more giant pandas in Scotland than Tory MPs.

England is dismantling the traditional welfare state through marketisation of the NHS, welfare caps and free schools, while Scotland retains faith in the monolithic health service, social security and universal comprehensive education.

Scotland will likely evolve into a relatively high-tax, high-spend oil-rich Nordic state within the EU, emulating Denmark or Finland. England may seek its own form of independence, probably leaving the EU to become a finance-led market economy with low taxation and diminished social protections.

Eventually both sides will realise that these increasingly divergent political cultures should accept their differences and seek a new and looser constitutional arrangement.

Iain Macwhirter presents Road to Referendum, a documentary on the national question on ITV, 19 August 2013, at 10.30pm