There was one political leader, more "phobe'' than sceptic, attempting to shred political and economic union, gleefully applauded by young devotees. Another leader, much more cautious, stressed the dangers of disruption to business, talking about the need for wider markets, harping on the threat to jobs. He looked less confident and was heckled more.
The scene was typical, in short, of a European debate at Westminster in these days of bitter Tory civil war. Except that in this case, there wasn't a Conservative politician present - and this wasn't London, it was Edinburgh. The Parliament wasn't the existing Thames-side one, but the promised Scottish one. The single currency, on the other hand, wasn't the promised European one, but the real British one, the pound.
The economic and political union, naturally, was the BU not the EU, and its enemy was Alex Salmond, leader of the Scottish National Party - a Britophobe, not a Tory Europhobe. Lastly, the serious-looking voice of moderation, standing up for business interests, was in fact a Labour leader, the Shadow Scottish Secretary, George Robertson.
This was the Scotsman-sponsored "great debate'' on whether Scotland should opt for devolution as proposed by Labour, or outright independence as fought for by the SNP. And it was a great, or at least fascinating, political event.
Comparing the two kinds of nationalism may seem odd. After all, Scottish nationalism is broadly left-wing, and English Tory nationalism is right- wing. The Scottish Nationalists have their own party, and the English nationalists don't, but they're working on it. Scottish Nationalists are fervently pro-European; the same cannot quite be said of Tory nationalists.
For it isn't just their opposite attitudes to the EU that divides the two nationalisms. There is something about English Tory nationalism that particularly grates on Scottish nerves. The assumptions of superiority, the tone, the spirit, is deeply inimical. There are hardly two British elected politicians who would agree about so little as Salmond and, say, Michael Portillo.
Yet the comparison between Scottish and English nationalism is real enough and carries an important message about the next election, particularly, as we shall see, about the main non-nationalist party.
Both the nationalisms are radical. They pose a populist challenge to the grey economic consensus and the `'common sense'' of business leaders, who fear disruption and isolation most of all, whether it be caused by refusing to join a single currency or by advocating the break-up of the BU.
The nationalisms regard aspects of the current order as illegitimate and point to the possibility of rebellion, which means, these days, civil disobedience. Lord Tebbit's remarkable remarks about Nelson Mandela and law-breaking closely match the views of hardline Scottish nationalists: if the voters of Scotland/Britain cannot reject the laws of Britain/Brussels, these laws lack the democratic mandate and can be broken.
Finally and crucially, of course, both nationalisms depend on a deep and challenged sense of belonging. Though they come clothed in the language of modernity, they are revivalist and emotional.
This correspondence in style affects the leaders, too. Salmond and Portillo might be poles apart in their political views, but they are superbly self- confident, aggressive performers and for the same reason. They draw on deep wells. They can send a shiver of delight through the faithful. And a shiver, period, through the timorous.
These nationalisms are like sisters separated at birth and brought up under different circumstances to believe different, antithetical things, to dress differently, to speak differently - yet whose little tics and silhouettes can, under the right light, strike the viewer with shocking force.
And they have one final thing in common, which may be the most significant matter of all. They both oppose themselves to Labour.
The Scottish Nationalists see Labour's devolution proposals as a Unionist plot. With some justification - Robertson told the Edinburgh audience that if he thought a Scottish parliament would bring about the end of the UK, he would be against it. Salmond noted that the Scottish Secretary and leader of the Unionist camp, Ian Lang, wasn't present - then added that, since George Robertson was there, he didn't need to be.
The Tories, meanwhile, accuse Labour of helping the Scottish Nationalists and preparing for the break-up of the UK. In last year's European election campaign, they attacked Labour as Euro-federalist, too - in effect, the Celtic-dominated enemy of English nationalism.
So it might seem that Labour is caught in a trap, with nothing much to say to either of the great emotional political movements roaring through the Scottish and English constituencies they need to win. It has no flags to wave.
But I think the opposite is true. This is not Labour's trap, but Labour's great chance. Despite the huge appeal of nationalistic anti-Europeanism, most English voters will be more alarmed than exhilarated by the possibility of a final exit from the EU. Compared to the warring and unpredictable Tories, Labour may look like the safe option.
Similarly, though the tide of nationalism is bubbling through Scotland again, history suggests that when it comes to the point, a suck-it-and- see devolved parliament may appeal more. Labour's plans for Home Rule, which are adventurous by any normal measurement, will again seem the safe option - even the dully sensible one.
The final twist to the story, however, is that Labour's plans would mean dramatic change - it is only the behaviour of its enemies that makes it seem grey. For me, this was summed up by the Edinburgh debate. There was Robertson, out-performed by the brilliantly sharp Salmond, sounding like a rather unimaginative fellow, warning that we shouldn't go too far with this constitutional business, that uncertainty is bad for jobs, and so on - and maybe picking up votes as he did so. And yet this is a man promising to create a new Parliament, radically different from the old one, in a few years' time.
Wouldn't it be a delicious joke if Labour, committed to the most drastic changes to the British political system since the arrival of universal suffrage, was elected because it seemed, by contrast with the Euro-sceptical Tories and the SNP, satisfyingly dull? It would be, as they say in Edinburgh, a real hoot. But as each day passes, that very outcome seems likelier.Reuse content