This situation is, he argues, a reflection of how poorly mainstream British politics has absorbed the implications of the Belfast Agreement. "The changes in Northern Ireland are very important because of the way they have changed the whole British constitution and the nature of sovereignty actually. But, Britain being Britain, this has not registered - there's no document proclaiming it. It has just happened and the nature of the citizenship of the people of Northern Ireland is now different.
It has undergone a transmutation from the traditional pattern which is going to be permanent and which affects everything else and can't be reneged on. It is permanent and the changes in Scotland and Wales are likely to be of the same kind. They're not so crucial as those in Northern Ireland but their long-term effects are likely to be as potent." They will be potent, argues Nairn, because the devolved institutions will inevitably acquire a kind of national authority. "The most likely development is towards a kind of de facto independence. It's not really clear that they will have to go towards the old-fashioned traditional model of nation-statehood. But they will have to become, in a de facto sense, independent. The anomalous constitutional model under which they are living leaves them no real choice except to go in this direction. They have even now too much power not to be constantly impelled towards assuming more and demanding more."
Those demands, he believes, will probably come to a head over Europe. For, while England remains deeply ambivalent about its relationship to the EU, the Scots and the Welsh are wholeheartedly committed to it. This division may well emerge in the coming years when, as promised, Blair holds a referendum on whether to abandon sterling for the euro. "What happens if the different countries within Britain vote in different ways? There's a very high probability of this happening. There would certainly be a strong majority in Wales and everyone assumes in Scotland too. But England is a whole other matter. And that's the thing that's most likely to precipitate a formal conflict between both the assembly in Wales and the parliament in Scotland on the one side and London on the other."
Not that he envisages the emergence of a new Scotland built on myths of Robert the Bruce and William Wallace or on the notions of ethnic purity that often fuel nationalism. For Nairn, the Scots biggest problem will be, not the English, but the Scots.
"Scotland is not an ethnic nation. It's an institutional nation. It's a kind of buriedalive state, more than a resurgent nationality. There's no nation to be built in Scotland. We did all that in the Middle Ages and then signed it away. But we don't have to do it again. What's happened is that under Thatcherism, the institutional class, which is Scotland's ruling class, moved over from unionism to a kind of quiet, creepy nationalism. They got their parliament and it is in a way another creepy, canny old Scotch institution like Glasgow or Edinburgh town council writ large. The problem for most nations that have achieved self-rule is what to do with the wild men with guns in the hills who have helped you achieve it. That's not Scotland's problem. The curse we're saddled with is the native, institutional middle-class with its over-regimented, canny culture of doing everything by the rules and never looking further than you have to. In that sense, we need to be liberated from ourselves."
After Britain, by Tom Nairn is published by Granta, price £15.99 in UK.