Consequently, the man who is in practice the King - Francois Mitterrand, President of the French Republic - is facing one of the toughest nights of his political life. In the amphitheatre of the Sorbonne this evening he will confront one of the treaty's most eloquent opponents, Philippe Seguin, a maverick from the neo-Gaullist RPR party, who has defied his party leadership and opposed the agreement. Mr Seguin, a skilful orator, has been pounding the campaign trail all summer long; Mr Mitterrand, reclusive at the best of times, will be hard pressed to match him.
None of this need have happened. Mr Mitterrand called a referendum on Maastricht because after the Danes rejected the treaty in their poll it seemed a neat idea. There was little doubt that the treaty would be approved, for France has been one of the most communautaire countries since the founding of the EC. The two main centre-right parties were divided, their leaderships pro-Maastricht but many of their rank and file opposed: they could be discomfited. Better still, Jacques Chirac and Valery Giscard d'Estaing, leaders respectively of the RPR and the UDF, would be forced to line up alongside Mr Mitterrand.
It remains to be seen whether this was another piece of masterful political mischief, or the worst mistake of the president's career. Last week the rise of the 'no' vote in the opinion polls duly brought Chirac and Giscard out into the open. They are now exposed to sniper fire from the anti-Maastricht right and can only turn to the left for assistance.
Yet if he wins this battle, Mr Mitterrand may lose the war for Maastricht. The French have a penchant for kicking their leaders in the teeth when things get bad. Mr Mitterrand's popularity is at a record low and the Socialists are beset by corruption scandals and election defeats. Long-term unemployment affects not just workers in sunset industries, but also skilled professionals. Now comes an excellent opportunity for the people to get their own back.
But Mr Mitterrand's miscalculation may have been even greater than this. Nobody expected the National Front or the Communist Party to vote for Maastricht: one regards it as an immigrants' bill of rights, the other as a bankers' charter. What Mr Mitterrand should have foreseen is the strong current of anti-Maastricht sentiment in the political mainstream.
The 'no' campaign has found support on the respectable right, and in particular in Mr Chirac's RPR, the party that is the (self-appointed) heir to General de Gaulle. It has been the vehicle for Mr Chirac since 1976, and he has steered it closer to liberal conservatism and away from its allegiance to the state as the vehicle for political achievement.
That the 'yes' campaign has had difficulty convincing the French public is not surprising. There is enormous confusion in France over Maastricht; more so than in Denmark, where the voters of a small state were well educated in the treaty's vices and virtues.
Mr Mitterrand hit a nerve by exposing the debate about Europe to general discussion. The 'no' campaign was quicker off the blocks: the 'yes' vote quickly descended from 70 per cent in the polls, and the 'no' vote climbed from 30 per cent to the point where they are evenly balanced.
The anti-Maastricht camp echoes the British right in its loathing of the treaty, but the accents are different. There is no question of hostility to the single market or the European Monetary System; the French right is solidly behind these things, as it is behind what it sees as the central purpose of the European enterprise: keeping Germany in check.
The concerns about Maastricht are many and various, from its monetary aspects to the future of Camembert cheese. But on the centre-right there is a fear - which Mr Seguin has brilliantly articulated - that it undercuts the links between French institutions and French citizens.
The most telling anti- Maastricht line is the use of the word 'technocracy' to describe Brussels and the Commission. This carries the same sentiments as the accusations in Britain of 'facelessness' - but it has an additional dimension.
Sovereignty, a concept to do with authority, is less a worry to the French than citizenship, the rights and duties that accrue to every French person through the Republic. In Britain the debate centred, above all, on the powers of the House of Commons. Mr Seguin is drawing on a tradition in which state, nation and citizen are intimately connected. He is reinventing Gaullism for the Nineties: a more populist version than Mr Chirac's, but one recognisably resonant of De Gaulle.
The Maastricht treaty, ironically, has for the first time put European citizenship into EC law. But it is a poor, weak thing, largely to do with holding a European passport and being eligible to stand for municipal office. A few scattered lines deal with citizenship; by contrast, the sections concerned with carving up powers between national governments, the European Parliament and the Commission fill page after unreadable page.
Many of the referendum themes echo earlier electoral battles in Europe and previous fights over the treaty: the rejection of the establishment; the long-ruling party disdained; economic distress aggravating political unhappiness; and a treaty that symbolises all this by seeming to cede power to an unelected minority. Then there is the use of fear to try to keep voters in line: with threats of German resurgence and financial collapse, the 'yes' campaign clawed back a few points in the polls last week.
France's 'no' campaigners have learnt from the Danes. Keep close to the ground; ignore the establishment warnings of chaos; assume victory is possible; let the other side make the mistakes. The 'no' campaign has cleared its first hurdle: it has become visible, credible and a feature on the political landscape. Its backing is wider than the traditional anti-European camp. It is a phenomenon that Mr Mitterrand has been forced to take seriously.
The next step is for the 'no' campaigners to engage those in the middle of the debate who fear a future without the EC, but have not been convinced by the arguments in favour of Maastricht. On 20 September they could yet turn Mr Mitterrand's political mischief against him.