The late political scientist Jim Bulpitt used to complain there was more work published on political failures than on the Conservative Party, which, after all, dominated Scottish politics until half a century ago.

As James Mitchell notes in his new book, The Scottish Question, Bulpitt was referring to the vast literature that existed on the politics of nationalism long before the SNP banished failure and started winning elections.

Indeed, with honourable exceptions - including works by Professor Mitchell - there is little on the relative success and endurance of the Union and Unionism. In this case, the victors have singularly failed to write their own history.

Even Gordon Brown, currently enjoying a new lease of political life thanks to the referendum, co-wrote The Politics of Nationalism and Devolution back in 1980, a little-known but cogent work cataloguing the then arguments for Scottish independence.

This week, with the publication of My Scotland, Our Britain: A Future Worth Sharing, the former Prime Minister balances out not only his own back catalogue but the constitutional literature in general, for it's an equally cogent contribution to the much-neglected case for the Union.

It's difficult to think of any competing volume from the other side of the debate. Alasdair Gray's recently published Independence: An Argument for Home Rule is more an eccentric mash-up of (bad) history and score settling than an "argument", while the recent Common Weal manifesto is admirably comprehensive but politically naive.

Mr Brown's tome is also an eclectic mix, although the interesting sections easily outweigh the bad. And although it draws significantly on the work of close colleagues like Jim Gallagher (now of Better Together), it contains much that is fresh.

Much of it builds on the idea - although not explicitly stated - that Scotland has always been, to varying degrees, "independent" within the UK and has, therefore, always possessed self-determination. It's just that, at least until now, it has self-determined in favour of the Union.

This, a much more nuanced and convincing depiction of the Anglo-Scottish Union than that posited by many supporters of independence, inevitably casts September's referendum question in a different light. Indeed, Mr Brown argues the Yes campaign is asking "for what we already have", ie, nationhood and independent institutions, while downplaying the consequences of severing long-held political ties.

He also recasts contemporary concepts of the UK, acknowledging that Diceyan notions of untrammelled Parliamentary sovereignty are "dead and buried", the Union being "closer to a covenant than a contract" and that therefore the ongoing quest for a "more perfect" devolution settlement will, "in effect", amount to a "new power-sharing agreement between Scotland and the UK".

Speaking at the Borders Book Festival on Saturday, Mr Brown alluded to a constitutional settlement that would come "as close to federalism as you can have in a nation where one part forms 85% of the population".

To my mind this is needlessly reticent, for the Brown plan (outlined at the end of his book) is federal in all but name: "devolution all round" (in England); replacing the House of Lords with "a senate of the regions and nations"; and codifying "the new division of powers and the new power-sharing, tax-sharing rules in a written constitution".

But as Martin Kettle observed in The Guardian last week, the fact that a figure as senior as Mr Brown is seriously considering federalism is significant in itself; as Alistair Carmichael remarked yesterday, it is a "logical conclusion" of the debate, yet all Mr Brown can bring himself to say is that "many federalists will support our measures".

My Scotland, Our Britain is rightly suspicious of conflating policy aims with constitutional reform, but at the same time it challenges one of the main assumptions at the heart of the pro-independence case: that only a Yes vote can deliver social justice. "The trouble," he observes, "is that achieving a big change in people's lives is somewhat harder than simply stating your aspirations."

Indeed, as I've argued before, the SNP's commitment to reducing inequality is largely a debating point. Mr Brown said in Melrose that the SNP were "dining out on a myth" that there existed an easy short cut to "some Valhalla for social justice", yet in the absence of any meaningful plan to tackle income inequality, sky-high bonuses and reforming property taxation then you merely end up "saying you want to do it without being able to pull it off".

This argument fuels his belief in the "pooling and sharing" at the heart of the UK, a phrase he now uses ad nauseam, although with good reason. Boldly, he takes this analysis further by arguing that far from reducing inequality, "an independent state which broke the arrangements to pool and share would be likely to see inequality rise" rather than fall.

Again the historical context of the "welfare union" is intriguingly recast, a consequence of Scots who "renounced and abandoned their own distinctive institutions to make it happen", while contrasted favourably with other countries, few - if any - of which have managed to create a similar set-up. In slightly hyperbolic terms Mr Brown argues that the British Union has evolved into a "progressive project quite without parallel in human history".

There are, of course, problems with a lot of this. Federalism, quasi-federalism or whatever one calls it, has - to say the least - implementation issues, while lauding the virtues of a redistributive union is trickier in the context of a Tory-Labour consensus about reducing the means available to redistribute (a point neither addressed nor acknowledged in the book). Mr Brown is also reticent when it comes to identifying a "British" national identity, obviously still bearing the scars from that particular project during his 13 years in government.

Nevertheless, a book-length re-evaluation of the Union plugs a sizeable intellectual gap. "Every generation of Scots has had to think through our relationship with England," he reflects, "and no generation has had to engage in more reflection and reappraisal than this one."

Today the three Unionist parties will set out a joint commitment to further powers in the event of a No vote. Inevitably there's a feint whiff of fudge about this, the declaration stating that "while the details of our plans differ, they all include a commitment to drive more taxation and social protection to Holyrood". Refreshingly, however, there's also an acknowledgement that the UK has, in the past, "got some things wrong".

This humble tone is arguably long overdue, as is the more positive framing of a potential No vote. In his book, Mr Brown concludes that "a multinational association that shares risks, rewards and resources is a beacon for the world of the future".

He declares: "I vote for Scotland leading Britain, not leaving it." It will be interesting to see how his opponents respond.