Then we will wake up. History will judge Sunday’s vote differently. After five decades of trying to turn Europe away from its old demons of populism, protectionism and passionate nationalism, they are about to rise up again with dangerous consequences for Britain’s national interest.

A moment’s reflection will show that it is impossible to devise a Europe that can satisfy Jean-Marie Le Pen, whose odious anti-Semitic and racist politics have shamed France for more than two decades, and at the same time keep anti-trade Trotskyists and public sector unions happy.

Soon we shall see the unravelling of the populist front against Europe. But first there will be a long and bitter period of recrimination and unhappiness as the fractured French political class seeks to find clear new bearings.

The French of both the rejectionist Left and Right were correct to criticise the new treaty as being excessively britannique. For the first time in five decades, Britain was in the driving seat of shaping the new treaty. The public face was Valéry Giscard d’Estaing, but the hand controlling the keyboard was Britain’s cleverest postwar diplomatist, Sir John Kerr. His genius in promoting core British interests has made him a star of the treaty-writing classes in Brussels, Washington and Paris.

The new treaty should never have been called a “constitution”, with all the grandeur and implied statehood that noble name implies. What it could not do — no more than the existing treaties — is force the governments of Europe to reform their economies and labour markets so that they corresponded to modern needs.

Despite claims to the contrary, Brussels is responsible for less than 10 per cent of the laws passed by nation states. Business regulations stemming from the single market have to apply across 25 member states but it is Paris, Berlin and Rome that are responsible for the unhappy state of their economies, just as it is London, Madrid and Dublin who have taken the decisions leading to job creation and growth in Britain, Spain and Ireland.

No one in Brussels was modest enough to admit the EU Commission — today employing fewer people than the BBC — was not a putative government of Europe. No one is Paris was brave enough to admit that the problems of the French economy and labour market were the fault of policy-deciders in Paris and had nothing to do with EU membership.

And so the Treaty has gone down to defeat. Every protectionist force in France will now be clamouring for relief from an onerous obligation to obey the common rules of Europe. Wine-growers in the Languedoc will want to slow down the import of Australian and Spanish wine. French ski instructors will now find justification for their campaign to stop their British counterparts from working in the Alps. Employees of state-owned airlines will find reasons why non-union Ryanair should not be allowed to fly at cheap rates all over France.

M Le Pen will now expect Paris to veto Turkish enlargement talks. Because what British Eurosceptics have never been adult enough to realise is that their dislikes about Europe are mirrored by equal and opposite dislikes in other countries. A Europe that is the sum of all the dislikes of Brussels is not a Europe in which good business is going to be done. Britain is a trading nation which has always sought a Europe of tolerance living under rule of law and respecting contracts freely entered into. The new treaty was an extension of law across Europe and it came about after lengthy negotiations before the final treaty was signed in good faith by Tony Blair, Jacques Chirac, Gerhard Schröder and other leaders.

This new rule book for Europe made sense to other parts of the world. A US Secretary of State does not want to deal with 25 competing European foreign policies. In Asia, in Latin America, even in Africa the concept of a union of nations breaking down barriers to trade and living under commonly agreed laws was seen as a good way forward.

On Sunday, the French delivered a mighty blow to that vision of Europe. Now we have to live under the rules of the existing EU treaties of Maastricht, Nice, Amsterdam, Rome and so forth with all the powers and privileges of a European Commission and the other Brussels institutions that British Eurosceptics profess undying hatred for.

A “no” vote in France may solve the problem of having a referendum here. But does it resolve the burning question of Britain’s relationship with Europe? The answer is no. The Labour Government will have to decide what approach it takes towards Europe. A French “no”, combined with the enduring economic and political weakness in Germany and Italy, leaves Britain as the undisputed success story in the EU.

The new European Union member states look to Britain for leadership as it takes over the presidency of the European Union in a few weeks’ time. Never has British leadership been so desired and needed across the Channel. Above all, Britain must make common cause with France. This moment of maximum French disarray is precisely when ministers, MPs and political parties in Britain need to offer the hand of friendship to France.

Sunday was a defeat for old Europe. We must shape a new EU.

Denis MacShane is Labour MP for Rotherham and was Europe Minister 2002-05.

Times Recommends

• And lo, he ventured forth . . .
• Lying to your children isn't a crime
• A single way to improve IVF treatment