IT comes as a surprise to my Scottish Labour critics, such as Lord Foulkes, who believe I am a dyed-in-the-fleece Nationalist, that the only party I have ever been a member of is the Labour Party.

Admittedly, it was a long time ago, in the late 1970s. I don't actually know when my membership lapsed; maybe it never did. Like most people who have been involved with the party, participation peters out as the sheer tedium of constituency politics numbs the soul.

But the hard fact is that the SNP today are more Labour than Labour ever were. The Scottish National Party are unilateralist and reject Trident, are opposed to market reforms in the NHS and reject the bedroom tax, UK welfare reforms and austerity budgets. They support free higher education, the European Union, the Social Chapter, social housing, green energy, open immigration, a living wage, public spending, comprehensive education and many other left-wing policies.

Yet metropolitan journalists and Unionists continue to claim that Labour in Scotland are fighting the good fight for social justice against a populist Nationalism that wants to put identity above class, and turn politics into a culture clash.

There was a striking illustration of this last week in two major speeches on independence: the first in Glasgow by the chairman of the Unionist Better Together campaign, Alistair Darling, and the next day, by Alex Salmond in Nigg on the Cromarty Firth. Curiously, it was Darling who concentrated on questions of identity, while Salmond based his pitch almost entirely on social justice.

Darling insisted that "making a positive choice for the United Kingdom is as much a matter of the heart as well as the head" and went on to expatiate on multiple identity, cross-Border migration, and how there is no contradiction between being patriotically Scottish and British. He stressed the benefits of the single market in the UK, and asserted that Scots were better off in Britain, but he didn't promise to roll back the clock on spending cuts or privatisation

Compare and contrast with Salmond's speech on Friday, billed as one of a series in which he will nail Unionist canards of "Project Fear" and make a cast-iron case for independence. Salmond insisted not just that Scotland could be better off as an independent country, but also that only a Yes vote can guarantee the continuation of social protections that are being dismantled in England. Not only did he promise to rid Scotland of the bedroom tax, Universal Credit and so on, the First Minister also promised to reverse the privatisation of Royal Mail, noting wryly that Unionists had claimed that it was independence that threatened the postal service.

Salmond has promised that in an independent Scotland, there would be a constitutional guarantee for a job and a home for every Scot – a bold boast that could backfire down the line as jobless or homeless Scots take an independent Scottish government to the European Court of Human Rights. And, of course, Trident would be scrapped.

Now, the conventional Labour explanation is that Salmond's social agenda is a "cynical ploy", as Better Together described his speech, by a First Minister who is losing the argument. With support for independence stuck at 30%, Salmond is throwing everything including the kitchen sink at the referendum. He is trying to buy a Yes vote by offering Labour Scots the Moon if they will only lend him their support.

The Labour leader, Johann Lamont, goes further and claims that the Salmond agenda is actually anti-working class because universal benefits such as free personal care and free university tuition benefit middle-class people as well as the less well-off. Labour is currently reviewing its attitude to these benefits – but is treading carefully. Wisely. The tuition fees policy was a major vote-winner for the SNP in 2011.

True, there did sometimes seem an air of desperation about Salmond's pitch for Labour votes. In Nigg, he used the term "Union" more often than Darling did in Glasgow. Indeed, the SNP leader now talks of not one, but five unions that Scotland will preserve after independence: the Union of the Crowns, the UK currency union, the defence union of Nato (sans Trident), the European Union and the social union. But he insists that the only way to address what he called the "democratic deficit" is to scrap the sixth union – political and economic union – and seek independence.

The key union here is the one he is usually most reluctant to define: the social union. He is not just talking about maintaining pensions, welfare benefits and the NHS, though those would all be included in the post-independence continuity agenda. Salmond also seemed to be talking about the moral union that Darling argued that only the present UK could maintain.

"Under independence," the First Minister declared in Nigg, "we will continue to share ties of language, culture, trade, family and friendship. The idea that these ties are dependent on a parliament in London is and always has been totally nonsensical."

Well, whatever else it might be, it isn't nonsensical to fear that trading and cultural ties might be affected by independence. There are very few instances of independence, in Ireland, America, Africa or Eastern Europe, that didn't involve some degree of disruption to the unions Salmond hopes to retain intact.

Even that Nationalists' favourite, the "velvet divorce" between the Czech Republic and Slovakia in 1993, involved a degree of turmoil. Initially, the two states intended to remain in a currency union, but within a few years had decided to scrap it and re-adopt their own currencies – prior, of course, to merger in the European Monetary Union. Ireland used to be a component of the UK, sending its MPs to Westminster, but after independence it became a very different country and cultural, trade, family and language ties were all put under great strain.

So it is perfectly understandable if Scots who like the social agenda being presented by Salmond are still worried about the disruption that departure from the UK might involve – the cost of setting up new institutions, breaking the chain of command in the armed forces, losing UK representation abroad, and generally worrying that there might be border posts at Gretna Green. Yes, I know the SNP insist there will be no border controls, but many Scots worry about England setting them up to keep out immigrants.

But the greater problem for Salmond is this: with all these five unions intact, can we still call this "independence" without robbing the term of any meaning? Don't get me wrong: we should commend the First Minister for his refusal to contemplate leading an independence movement that is based on cultural, ethnic or racial chauvinism. He is not some "Little Scotlander" who wants to keep the world out. And it is admirable that Scottish Nationalism is based on egalitarian and internationalist values. But it does mean that there is, paradoxically, a cultural hole in the Nationalist case. What Salmond seems to want is a better Union rather than a new country, and to many people, leaving the UK will seem like a rather roundabout way of achieving that end.