FRANCE appears to have rejected the proposed European constitution, throwing the EU into crisis and undermining Tony Blair's plans for a similar vote in the UK.

Exit polls released as polling stations closed last night suggested that the French had rejected the constitutional treaty by a margin of 55 per cent to 45 per cent.

If confirmed, the result would throw into doubt a UK referendum, due to take place in spring next year, because the ratification must be unanimous.

Tony Blair has said that the referendum would go ahead as long as there was still a treaty to vote on.

But defeat in France - expected to be followed by a similar result in the Netherlands on Wednesday - could be enough to kill the treaty off, particularly since Paris has been one of the main drivers behind the European project.

Mr Blair, who is enjoying a weekend break in Italy, is expected to give his reaction to the French vote today, but it is not known whether he will give an immediate indication on the future of a British poll.

It is thought he will hold talks with fellow EU leaders ahead of a planned summit of the European Council in Brussels on June 16, when they will decide on a way forward.

The decision about whether to try to salvage anything from the treaty could now overshadow Britain's six-month presidency of the EU, which begins on July 1.

British supporters of the constitution were left in a despondent mood. Lucy Powell, campaign director of Britain in Europe, said: "If the exit polls reflect the final result, then this is very disappointing.

"It is clear there were many factors at play in this referendum - domestic issues, as well as concerns over enlargement and the perception that the treaty is too Anglo-Saxon - all played a role.

"We still believe that the treaty is in the best interests of Britain and Europe but, clearly, it will now be up to the European Council to find the appropriate way forward."

Labour's former Europe minister, Denis MacShane, said: "British pro-Europeans must learn the lesson of the victory for the 'no' camp in France. The rejection of the constitutional treaty will unleash protectionist and isolationist political and economic forces in France and elsewhere in Europe.

"Today's Europe needs economic reform to create jobs more than it needs political projects like the new treaty.

"The European Union will continue to function under the existing treaties of Maastricht, Nice and Rome. We will now see a period of stasis as Europe digests this result and we wait to see if elections in Germany this year, Italy in 2006 and France 2007 provide new leadership capable of shaping a Europe of growth and social justice.

"Britain should be at the forefront of defending this European Union, which must be in tune with its citizens but not surrender to populism and protectionism."

All 25 EU nations must ratify the treaty for it to come into effect. Nine have so far ratified the treaty, eight by a parliamentary vote and only one - Spain - by referendum.

France is the first country to vote down the treaty, but observers believe that its decision could have a domino effect on later referendums planned in the Netherlands, Poland, Denmark and Britain