Spending time in the United States is a sobering reminder that when it comes to the United Kingdom, nomenclature is tricky.

Telling someone you’re from the UK rarely hits the mark, though “Britain” fares slightly better. More often than not, the default setting is simply “England”, and while Scotland does register as a distinct entity, it’s often confused with Ireland.

In political terms, the contested nature of the UK also leaves Unionists grasping for suitable terminology. For understandable reasons, no-one uses the state’s full name (United Kingdom of Great Britain and Northern Ireland), while the “Great” is usually shorn from “Britain”.

But when even that is questioned – some Nationalists speciously argue that “Britain” is a geographical rather than a political term – the matter still isn’t resolved. Indeed, some supporters of independence even refer to “these Isles” to avoid uttering the dreaded “B” word.

A new pro-Union “forum for debate”, which launches in London tomorrow, clearly bears the imprint of similar angst. “These Islands” (its logo, interestingly, includes the whole of Ireland) boasts an impressive advisory panel and a mission statement standing “unabashedly for the view that more unites the three nations of Great Britain than divides them”.

This, frankly, is long overdue. While the “No” side won the 2014 referendum, it was clear at the time that having been unstated for so long, the Unionist argument was strong in utilitarian terms but existentially weak, a sort of mirror image of a Yes campaign that lacked a credible economic rationale but owned the crucial narrative of what constituted “Scottishness”.

These Islands is not only politically ecumenical, but appears to be keeping its distance from the UK Government and Unionist parties (one minister I spoke to had no idea what it was). This makes sense. Unionist arguments, much like Nationalist ones, often end up stymied by too close an association with a particular political party.

The organisation has three “leading themes”, the first of which is the “moral case” for the Union. This strikes me as a bit of a minefield, for the trouble with making “moral” arguments for a particular constitutional settlement, ie independence, is that it’s highly subjective and often spills over into sanctimony. These Islands speaks of renewing the Union’s “liberal idealism”, which is a noble aim, though most likely a quixotic one.

It’s on stronger ground when it comes to the second theme, “issues of identity”. In spite of recent events, a feeling of Britishness remains important, as acknowledged by the SNP’s (unconvincing) attempts to co-opt it during the independence referendum. These Islands reminds us, correctly, that Britishness was the original “civic” identity, inviting adherents from all corners of the Union and beyond. Furthermore, Unionism has always celebrated diversity rather than attempting to suppress the UK’s various nations and nationalisms; “the embodiment of the idea, since put to good use by the United States, that from the many – one”.

Revealingly, the last of These Islands’ themes is the economic case, where it promises to provide “rigorous” analysis of “the UK single market”, another entity that’s contested in certain quarters. Last week the SNP MSP Joan McAlpine (“the gift that keeps on giving”, according to a Tory opponent) even denied its existence then, in a letter to this newspaper, denied having denied it.

While of course any established nation state possesses a single market, it remains accurate to describe the UK’s as such. In 1707 Scotland joined the larger English (and colonial) market, as did Ireland in 1801. And, in 1921, the Irish Free State left that single market, as would Scotland had it voted “Yes” in 2014.

It is, contrary to Nationalist orthodoxy (I spoke to a special adviser recently who also denied its existence), a real and living thing with considerable advantages for Scotland, certainly more so in terms of trade and GDP than its European equivalent. It also includes a single currency which, if reports of the SNP’s Growth Commission are accurate, would be disrupted by the adoption of a new “Scottish pound”.

Nevertheless, the ongoing Brexit psychodrama clearly represents a challenge to contemporary Unionism. Make any argument in support of the UK, however good and true, and the inevitable rejoinder from opponents will be “but what about Brexit?” That, of course, masks innumerable contradictions, yet in crude debating terms it constitutes a significant weakness in any reinvigorated Unionist case.

But while the SNP appears to be banking everything on a Brexit catastrophe to deliver victory in a second independence referendum, in fact the main battleground remains economic. At the same time, Unionists clearly have work to do when it comes to prosecuting the utilitarian aspect of their case with more clarity and enthusiasm.

Through a relentless drizzle of misinformation and low-level conspiracy theories, for example, the Scottish Government has managed to render its own annual GERS figures as a matter of opinion rather than incontrovertible fact. That has to be challenged, for fiscal transfers (that undeniably benefit Scotland) are as real as the UK single market.

These Islands is obviously aware of this, promising to “ensure that the provenance, reliability and limitations of data relevant to the future of the United Kingdom is clearly laid out”. Usefully, however, it takes care not to rest on its laurels, accepting a “pressing need for recalibration”, reviewing and, where necessary, renewing the constitutional status quo. “Nationalism, populism and division are not inevitable,” it concludes. “There can be a better future.”

As last year’s European referendum tragically demonstrates, if you don’t make the case for a multi-national Union, then you can’t expect voters to carry on supporting it. The same is true of the United Kingdom, Britain or “These Islands”, whatever you choose to call it, the nomenclature is less important than the argument.