Andrew Marr and Tom Nairn have produced books on an almost identical topic: the growth of nationalism in Britain and the likely breakup of the United Kingdom. It seemed an obvious pairing, yet few papers made the connection. Nor did they ask their political heavyweights to assess the daunting thesis - that our current political arrangements are unsustainable. Perhaps the burlesque of the London mayoral race has diverted eyes from the more important issues.

Of the two, Andrew Marr's The Day Britain Died (Profile Books, £7.99) gained more attention (the fact that it was backed by a TV series may have helped). Marr is one of Britain's - we can, presumably, still use that term - most insightful commentators, as fellow pundit Matthew Parris made clear in the Times. "When one learns that the author has 'travelled around the country', 'meeting people', the heart sinks," he wrote. "Meeting which people? Who chose them? Why? But then the eye moves to the author's name: Andrew Marr. The heart lifts. This will be the product of a real mind, a singular literary flair, an integrity still intact. Such an author is capable of stamping a book - maybe even a television series - with an idea."

And, he concludes, Marr has. "Shorn of the many intriguing sideways insights the author provides, the central idea is simple, powerful, and finally persuasive: Englishness exists. England's senses of itself go back more than a thousand years, albeit in different forms, and unless England is recognised and given a new sense of its own security, then all hopes for a liberal, open, democratic and tolerant future are in danger... Yet England has been pushed into a corner where it is expected to passively await its future. That, in itself, is dangerous."

Parris's focus on that strand of Marr's book was perhaps a little perverse: the view from north of the border looked rather different. "What does it mean to be British, he asks. The answer: not a lot," wrote James Robertson in Scotland on Sunday.

"Almost nothing to most Scots, nor, in fact, to the people hardest hit by the disintegration of the 'British' label, those for whom it has been a threadbare safety net against racism. Many who immigrated between the 50s and 70s, who came as a consequence of the historical fact of empire, now find that the identity they thought was theirs to put on has been discarded by others in favour of Scottish, Welsh and even English ones.

"The term 'British', it is now clear, was created and sustained for only one reason: the empire. Without the empire, it is redundant. Marr puts this into a wider context: the Americanisation of the world; the growth of Asian and Pacific economic power; the end of Communism and the new Europe. Identity is flexible now: all of us have become Europeans and Americans to some extent in the way we live our lives."

Several reviewers mentioned that the book had evidently been written in a rush (Marr admitted as much in the introduction). "This book, at first, feels deadeningly over-familiar," wrote Andy Beckett in the Guardian. "Andrew Marr has produced - at speed - a volume heavily reliant on quotes from his fellow pundits and polemicists. Here are half-page sections and hurried references from Jeremy Paxman's The English, Peter Hitchens's The Abolition of Britain, Simon Heffer's Nor Shall My Sword: The Reinvention of England - all recent books, all concerned with the temperature of the nation in the early fevers of devolution, and all slightly patched together, short on original fact and thought."

But Beckett quickly warmed to the book, especially when Marr took to the road and started to quote the opinions of anxious Brits. "The Britain that emerges is mixed-up, complicated, and 'in a state of constant flux'," concluded Beckett. "The supposedly cruel capital, for example, absorbs immigrants more easily than allegedly friendlier regions. The English patriots of the Home Counties know more about Normandy than the north of England. The idea of Englishness itself, Marr suggests, may never, at any time, have meant the same thing to everyone.

"His writing relishes these tensions and contradictions: English tabloid culture is neatly summarised as 'swagger and self-pity'; the 'strange, sharp flavour' of modern Britain is crisply evoked. Marr concludes that only a federal country, with separate parliaments for each of its parts, can hope to hold such a hybrid together. He fears a complete break-up, interestingly, for the squeeze it might put on minorities."

Meanwhile, Tom Nairn's After Britain: New Labour and the Return of Scotland (Granta, £15.99) got shorter shrift. A ponderous review by T M Devine in the Times found the book "eloquent and sophisticated" but had difficulty explaining why. "We may indeed be seeing the first stages of a general reconfiguration of relationships within the British archipelago which, inter alia, disperses power from Westminster and by so doing maintains the political links between England and Scotland," wrote Devine.

"If London can respond positively and sympathetically to such a dynamic, the best bet for the future is probably a framework of federalism, rather than 'Scottish independence' in the classic form delineated in Tom Nairn's stimulating book." I think the publicists will just be satisfied with the word stimulating.

Bernard Crick, in the Independent, was less well disposed to Nairn, dismissing his notion that the Scottish people felt the gaping wound of their lost state as "romantic nonsense". "Nairn, amazingly, is an old-fashioned sovereignty man," Crick pointed out with a nice touch of irony. "The British state is worn out, so therefore a Scottish state is needed."

There was a more generous review in the Observer. "Nairn is certainly a beast seen as fleetingly in these northern islands as the Arctic char or the wild cat - a genuine native intellectual... Nairn is in vintage form, shaking and sharp. He sees the coming English parliament clearly... This is, in short, the most intelligent book on the future of our states." So, take that Andrew Marr - you probably thought yours was the number one end-of-Britain tome. But who was the Observer reviewer who declared Nairn the winner on points? You have no doubt guessed: Andrew Marr himself. What a hero.