One in four French voters are ready to support the far-right National Front in next year's European elections, a new poll shows.

A survey of voting intentions for the May 2014 election found the party could win more support than the government and the main opposition party.

It is the first time in French political history that the Front National, led by Marine Le Pen, has headed a poll for a national vote.

The pollsters Ifop found 24% of the 1,893 French voters questioned said they intended to vote for the anti-European Union, anti-immigration National Front, while 22% said they would vote for the centre-right Union for a Popular Movement (UMP) and 19% for the governing Socialist party.

"For the first time in a poll on voting intentions in an election of a national character, the [National Front] is clearly ahead," Ifop said.

The boost for the party comes just 10 days before the second round of a byelection in the canton of Brignoles, in the Var, southern France, in which the National Front candidate gained 40.4 % of votes in the first round.

It also came as Alain Delon, one of France's most celebrated actors, expressed his sympathy for the National Front and said he "approved" of the party's rise. Delon had previously voiced his "friendship" and "liking" for the party's founder, Jean-Marie Le Pen.

In an interview with the Swiss paper Le Matin, Delon, said: "For years Le Pen father and daughter have fought, but they've fought somewhat alone. Now, for the first time, they're not alone. The French are with them."

The Nouvel Observateur magazine that published the poll on Thursday said the results were not a prediction, but the figures show a remarkable rise in support for the National Front. In the last European elections, in 2009, the far-right party obtained 6.34% of votes.

"The French are showing a wish to take their destiny into their hands and give back their country its sovereignty," said the Front National secretary general, Steeve Briois. He promised an "unprecedented earthquake" in the European elections.

In the Nouvel Obs, the French president, François Hollande, explained that the rise of nationalism and popularism in Europe was linked to "the fear of decline", "relations with Islam", and an ageing population. He said nationalism came from a "lack of perspective and collective dynamic".

Hollande, whose popularity continues to decline, admitted on Wednesday that there was a risk that the European parliament would have a "large share of anti-Europeans" after next May's election. "It would be a regression and a threat of paralysis," he said.

Marine Le Pen, a practising lawyer, has threatened to sue anyone that calls the National Front an "extreme right" party, a threat that did not seem to worry Hollande. "Faced with extremists, the best thing is to hold one's head high," he said.