The scene had been carefully set in advance. Pinned on the wall behind Marine Le Pen on election night on Sunday, at the party's headquarters in the Parisian suburb of Nanterre, were posters with the words: "The National Front: first party of France".

The National Front's score in the European elections, even if predictable, is spectacular and deeply shattering for the French political landscape.

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With 24.85 percent of voters, not only did the National Front (FN) win the elections for the first time in a nationwide ballot, but it arrived well ahead of the centre-right UMP, which is supposed to be the main opposition party. With only 21 percent of the vote, the UMP was pushed into second place while the governing Socialists managed a humiliating 14 percent.

But is it honest to brand the National Front as the "first party of France" as Marine Le Pen repeatedly did on Sunday?

Many voices have been heard trying to minimise Marine Le Pen's victory.

The main argument is that Le Pen's party received fewer votes (around 1 million fewer) than in the 2012 presidential elections. Given the levels of abstention this is true, as it is for almost all parties. But the National Front still quadrupled its score compared to the last European Parliament elections.

As a result the National Front has increased its presence in the EP from three to 24 seats, holding a third of France's 74 seats.

Another argument used to minimise the results is that high abstention supposedly favoured the far-right anti-EU party. But a survey by Ipsos-Steria, showing that mobilisation among FN electorate was only slightly higher than other parties, undermines this analysis.

Still, European elections are not local or presidential elections and analysts agree that the EP results are a turning point in France's political life. Much more so than the already unprecedented local elections in March, when the Socialist party suffered heavy losses and the National Front won 11 mayoral posts.

This time, the FN won the most votes in five of France's eight EU voting regions and came top in 71 electoral departments, compared with 28 for the UMP and just two for the socialists.

The FN is especially successful among young people. It received 30 percent of ballots cast by voters under 35 although the abstention rate amongst this group was 73 percent, according to polling institute Ipsos-Steria. The proportion of over 60-year-olds who voted for the FN is comparatively low (a fifth).

Unemployment is at record levels, and President Francois Hollande's attempts to reboot the country's economy have had very little effect.

The FN is especially successful among those groups that used to be in the Socialist camp: 43 percent of blue-collar workers and 38 percent of office workers voted for the FN.

To understand how dramatic the increase is among this group, let's consider by comparison the Socialists – they picked up just 8 percent of the blue-collar vote and 16 percent of the office worker vote.

Next stop the Elysee?

As a result, according to many analysts, the question is no longer whether Marine Le Pen will be able to reach the second round of the next presidential election, but who from among the other parties will be facing her. This is a profound change.

One socialist parliamentarian who saw Mr Hollande on Monday reported him as saying: "I expected it to some extent, but it was still a big shock."

Several factors led to the FN's success: French scepticism towards the EU, increased by the eurozone economic crisis; the absence of a charismatic personality in the pro-EU camp; a campaign monopolised by populists and by extremist rhetoric; a general malaise in France regarding the question of national identity and profound distrust of State institutions.

Last, but not least, is the weakness of the two largest parties, with an unpopular Socialist president and a UMP that vacillates between its republican wing and the temptation to adopt an extremist position.

Much will now depend on the attitude of UMP and the Socialists in the coming weeks and months. Following the results, both parties – left and right – had no other choice but to acknowledge their heavy defeat.

How will the traditional mainstream parties act now?

In a televised address to the Nation on Monday evening, French president Francois Hollande considered the results as "a vote of mistrust towards Europe".

He also promised to tell EU leaders at a meeting on Tuesday evening in Brussels that they must now focus on growth, jobs and investment, not on austerity.

But he also stated that the government would not waiver on its plans, and would continue with economic, social and territorial reforms, despite growing discontent even within the president's camp.

Following the results, French MP Julien Dray urged Hollande to seek stronger alliances with France's scattered left-wing political parties. This demand has been steadily growing within the party recently, but with little effect yet.

As for Manuel Valls, the Socialist prime minister, he called it "a shock, an earthquake". But given that he was only appointed a few weeks ago, in the wake of the Socialists' local election defeat, he refuses to bear the responsibility for the result.

Valls told French RTL radio on Monday that he would try to speed up existing plans to lower income taxes for France's lowest earners. "This tax system weighs too heavily on the lower and middle classes," he said.

As for the UMP, supposedly the main opposition party, it is in open crisis.

Under pressure from several UMP party heavyweights, party leader Jean-Francois Cope resigned on Tuesday, rocked by a corruption scandal over invoices for former president Nicolas Sarkozy's election campaign.

Already criticised for being unable to tackle the National Front's progression, the party is at a turning point. Will this resignation (effective on 15 June) mean a fresh start for the UMP?

There are many questions that must be solved before the next presidential election in 2017.