On Sunday, the French vote in a referendum on the EU Constitution - and polls suggest a Non is the almost-certain result. Nick Morrison looks at what is at stake as the EU faces its greatest challenge.

FOR 50 years, France has been at the forefront of the European project. One of the six founder members of the Common Market, France stamped its mark on the embryonic institution, and, as one half of the Franco-German axis, it has played a dominant role in pushing for greater integration.

Many of Britain's "difficulties" with the EU have revolved around France, from General de Gaulle vetoing Britain's application to join in the 1960s, to disagreement over the Common Agricultural Policy, the EU's biggest single chunk of spending of which France is the chief beneficiary. It's no surprise that much of British unease over the direction of the EU comes from a suspicion that it is a French hand on the European tiller.

But now the French are in danger of scuttling their own ship. On Sunday, the French go to the polls to vote on the EU Constitution, and all the indications are they will say Non. In the final days of the campaign, the No side has had a lead of six to eight per cent, and yesterday the leader of France's ruling party admitted the vote will be lost.

If the opinion polls are right, it will represent the biggest-ever setback to both the theory and practice of European co-operation, as one of its prime movers resists further integration. So why are the French likely to vote No, and what does this mean for the EU's future, and for our referendum on the constitution, expected next year?

Q What is the referendum about?

A The referendum is on the draft EU Constitution, which was drawn up by a convention headed by former French president Valery Giscard D'Estaing last year. The aim is to simplify the complex arrangements which govern the EU and are set out in a number of different treaties, by bringing them under one treaty. This is held to be necessary to cope with the EU's expansion from 15 to 25 states last spring. Without these changes, its supporters argue, the EU would be too cumbersome and unable to take decisions.

The constitution allows for greater majority voting and will extend EU influence into areas including justice policy, asylum and immigration. The European Council will elect its own President and will appoint a Foreign Affairs minister and the EU will draw up its own foreign policy.

Although the President will have more influence than at present, the post will still be subject to the Council and will have limited powers, and the Foreign Minister will be able to speak on the EU's behalf only when there is an agreed policy. Each country will retain the right to have its own foreign and defence policy, as well as a veto on taxation policy.

The constitution also means the European Parliament has to approve any decision taken by majority voting, and creates a "legal personality" for the EU for the first time, meaning it can enter into international agreements, a right enjoyed by its forerunner the European Community.

Q Why are so many French hostile to the constitution?

A One of the principal reasons many people are thinking of voting no is because of dissatisfaction with the French government and president, Jacques Chirac. Unemployment is running at around ten per cent and the economy is performing poorly. Historically, electorates have used referendums as an opportunity to punish an unpopular government, and that is partly the case here.

But there is also some unease over where the EU is going since last year's enlargement, particularly towards a more liberal economic path. It is feared that this could both open up French labour markets to cheap workers from eastern Europe - the "Polish plumber" has become a bogeyman in the referendum campaign - and undermine traditional French levels of social protection. The EU is also due to open entry negotiations with Turkey in the autumn, and there is widespread hostility to Turkish membership. Encompassing all these is a fear that France has been losing influence since enlargement, with many of the new members thought to be more sympathetic to Britain's point of view. The constitution itself is not particularly the issue.

Q What happens to the constitution if the French vote no?

A The constitution must be ratified by all 25 member states to come into effect, so if one state does not ratify it then it will fall. According to its backers, there is no Plan B, although there are other options. One would be to tack parts of the constitution onto existing treaties, although these may need to be put to a referendum in some countries. Some measures could also be brought in by agreements at the European Council, made up of the heads of government. But the constitution itself is likely to be dead, and France is unlikely to re-run its referendum, as Ireland did after initially rejecting the Nice treaty in 2001. It is possible there could be negotiations for a new constitution, but Giscard D'Estaing, who drew up the document, has said it cannot be improved upon, and it would also open up fears that other countries could demand changes by threatening to withhold approval.

Q What about the Dutch referendum?

A The Dutch hold their own vote on the constitution on Wednesday, and opinion polls show a substantial majority are planning to vote Nee. As another of the six founding members of the Common Market, Dutch hostility to the European ideal is as surprising as that of the French, but is largely a result of tensions over immigration and the cost of EU membership, as well as unhappiness with the government.

The Dutch poll is purely consultative and not binding, although politicians said they would take the result into account when voting on the constitution. But, unlike in France, if the Dutch vote No, then another referendum is likely, although if the French do vote No and the constitution is considered dead, then the Dutch poll may not go ahead anyway.

Q What does it mean for Britain's referendum?

A Tony Blair's announcement last year that Britain would hold a referendum on the constitution was initially seen as reckless: how could he hope to win a vote on Europe with a largely Eurosceptic electorate? But it was a clever piece of political strategy, effectively neutralising Europe as an election issue.

A No vote in France would seem to be the best solution for the Prime Minister, absolving him of the need to hold what looks like an unwinnable referendum. But there seems to be some confusion in Government. Europe Minister Douglas Alexander last week quoted Mr Blair in the Commons saying that the British people had been promised a vote and would get a vote, but the same day Foreign Secretary Jack Straw suggested that the referendum would not go ahead in the event of a French No. If Sunday's vote does mean the end for the constitution, as seems likely, then the Government is expected to ditch its commitment to a referendum, on the grounds that, as Mr Blair said last month: "You can't have a vote on nothing".

It could also affect the timing of the Prime Minister's departure. It was widely expected that the British referendum offered a perfect opportunity for Mr Blair to bow out, either as the acclaimed winner of a vote on Europe, or retiring gracefully after an electoral bloody nose. Such considerations will be removed from the equation if the referendum is scrapped.

Q What happens next for the EU?

A Confusion over the British response to a French No reflects confusion over what the next steps are for the EU. In theory, the EU could function with its existing treaties, and a European Council meeting next month will decide on whether to try and resurrect the constitution, or to have a six-month cooling off period.

But this could see the EU bogged down in decision-making, as each of its 25 members doggedly pursue their own national interest. One option is the launch of a "core" Europe, a small group of states which would press ahead with its agenda without needing to get unanimous agreement, but in the wake of a French No then French involvement would come more out of desperation than idealism. Although a No could undermine France's influence in the EU, it may bolster the French position, by putting pressure on the EU to produce policies more attractive to French voters.

But the real significance could be not so much derailing attempts to streamline how the EU works, but in delivering a psychological blow to the European ideal. If one of its founder members and one half of its leading duo is unhappy with where the EU is going, it raises serious questions about not just the pace but the direction of European integration, and poses major challenges for Europe's leaders in making the EU matter to its citizens.