In his introduction to a new edition of Geoffrey Barrow's classic text Robert Bruce And The Community Of The Realm Of Scotland, the historian Michael Brown notes that William Wallace is depicted not as "a popular leader of proletarian nationalism" but a figure who was "politically and constitutionally ...

conservative". In other words, Wallace and his associates sought to maintain or recover existing rights rather than overthrow established relationships.

By contrast, observes Brown, Edward I and his officials were the real revolutionaries, seeking to impose the English King's sovereignty over Scotland in novel ways. Meanwhile, Robert Bruce, in Barrow's account, believed the "maintenance of the Scottish realm outweighed issues of faction". By highlighting the idea of the "Community of the Realm" in the late 13th and early 14th centuries, Barrow (who died last week) gave it a contemporary significance.

Thus the idea that the Scottish people are "sovereign" rather than Parliament or the Crown continues to underpin modern Nationalist thought. But in a modern context sovereignty is one of those slippery concepts that resonates more in theory than practice. Alex Salmond uses the word a lot, although his vision of Scottish independence makes him, like Wallace, something of a conservative, albeit one imbued with Bruce-like notions of Scotland as a "community".

The White Paper's concept of sovereignty, like the First Minister's, is curiously old-fashioned. It refers repeatedly to the "central principle of the UK constitution" being the "absolute sovereignty of the Westminster Parliament". This it contrasts with "the sovereignty of the people of Scotland", the "central principle in the Scottish constitutional tradition". Such thinking, however, is at least four decades out of date. AV Dicey, who first outlined the principles of Parliamentary sovereignty in the late 19th century, would be proud.

In practice, however, the notion of "absolute" Westminster sovereignty has been on the wane since 1973, when not only did the UK join the European Economic Community (thus ceding sovereignty to a wider union) but also sanctioned a "border poll" in Northern Ireland. In a precursor of next year's independence referendum, the latter invited the people of the six counties to choose their constitutional future (in or out of the UK) via a referendum. Thus Westminster conceded that the province was sovereign, as in fact it had been since opting out of the Irish Free State some 50 years before.

Similarly, the devolution referendums of 1979 and 1997 acknowledged sovereignty in Scotland and Wales. Indeed, throughout the 20th century Parliamentary sovereignty was ceded repeatedly. The tiny Sultanate of Brunei only became independent from the UK in 1984, while this year David Cameron has emphasised the sovereignty of Crown subjects in the Falklands and Gibraltar.

In the White Paper's Q&A section, number 529 asks, almost innocently, "What does 'sovereignty of the people of Scotland' mean?" It means, answers Scotland's Future, "the people of Scotland have the right to choose freely their form of governance". Yet has this ever not been the case? Surely Scots could have chosen independence, via the ballot box, at any point since the SNP was formed in 1934; it's just, thus far, they've chosen not to. An expression of sovereignty does not depend upon a referendum); after all, the SNP has only advocated one for the past decade or so.

The concept of "Crown in Parliament", adds the White Paper, "means that the Westminster Parliament has ultimate power to do anything that it decides, including to overrule the Scottish Parliament on any matter". That is true, but again only in theory, and of course the Scottish Government would be hard pressed to find an example of Westminster exercising that right. On the contrary, the "sovereign" UK Parliament has been remarkably willing to dispense with its powers since 1999, most recently in the Edinburgh Agreement.

Of course, in crude political terms it suits certain Nationalists to depict Westminster as centralist and inflexible on sharing sovereignty, even though the Scottish Government isn't exactly a fan of devolving power beyond Holyrood's concrete walls. As one ministerial aide once put it to me: "Scotland is our localism", as if to say: thus far and no further.

The late Sir Neil MacCormick had a subtler grasp of post-1973 sovereignty in a UK and European context. He talked about the "post-sovereign state", arguing that four decades of European integration had replaced the absolute sovereignty previously exercised by EU member states with a more pluralistic arrangement in which new rules bound together those states at the European level, therefore removing certain powers previously exercised nationally. The same, of course, would be true of a "sovereign" and therefore independent Scotland.

In more thoughtful moments, Alex Salmond acknowledges this. "The resumption of independence is the resumption of political and economic sovereignty," he reflected a few years ago. "How you then choose to exercise that sovereignty reflects the inter-relationships with principally the other countries in these islands." Thus, even if an independent Scotland chose to leave its currency in the hands of the Bank of England, remain in the EU and maintain a UK-wide energy market, Scotland would be making that decision, not Westminster.

To supporters of independence this is no mere abstraction, but central to how they perceive an independent Scotland, even one maintaining close links with the rest of the UK. But in practice, as Ireland and various southern European countries have discovered since 2008, sovereignty can be restrained by all sorts of factors, not least financial meltdown; the logical extension of claiming, as the Independence Declaration does, that "it is fundamentally better for us all if decisions about Scotland's future are taken by…the people of Scotland", is for Scotland to leave the European as well as the British Union.

Yet at the same time I've long thought the "Westminster system" (as the White Paper insists on calling it) could afford to be a little more imaginative on the distribution of sovereignty within the UK. After all, the British Isles have long sustained several sovereign entities, so why not, as Welsh Conservative David Melding has suggested, formally "divide sovereignty between the home nations and the British state"?

Rather than being a bold departure from British political practice, it would acknowledge the reality of the quasi-federal status quo: that the peoples of Scotland, Wales and Northern Ireland are already sovereign within their territorial boundaries. Recognition of sovereignty need not result in fragmentation of the British state. In the United States, where there are three "parallel" sovereign entities (the federal government, states and Indian reservations) secession is regarded as unthinkable. Intriguingly, the SNP's 21st-century version of Bruce's "community of the realm" could be forged within the UK.