By Ingrid Melander

PARIS (Reuters) - Britain's vote to leave the European Union looks like a boost for France's eurosceptic National Front, but that could turn to trouble for the party if voters see instability across the Channel when they elect a new president in 10 months' time.

National Front (FN) leader Marine Le Pen looked ecstatic as the Brexit result was announced, calling it a "victory for freedom" that would soon be repeated in France, an EU-founding member whose voters are increasingly eurosceptic.

As the only major party in France that backed Brexit and is calling for a similar in-or-out referendum on EU membership, the FN has at first glance much to gain from a vote that thrust Europe to the center of France's 2017 election debate.

"It's excellent news for the FN," the party's vice-president Florian Philippot told Reuters. "Up until now we were told that leaving the EU would be apocalyptic, that we'd be isolated. Britain will show it's exactly the opposite."

Like many of the Brexit campaigners, the FN banks on grassroot anger with elites, and is faring well in small towns and rural areas that feel forgotten by globalization, giving it hopes the Brexit vote will push even more working-class voters to vote for it next year.

Opinion polls already show that the anti-immigration FN, whose ratings benefited from Europe's refugee crisis, is likely to top the first round of the presidential election.

"The headlines are doing the FN's job for it, yet again," said sociologist Sylvain Crepon, an expert on the FN at the university of Tours.

But where the Brexit legacy stands as the French vote for a president on April 23 and May 7 next year will be key.

The Brexit vote has plunged Britain into political chaos. Prime Minister David Cameron announced he is standing down, opposition leader Jeremy Corbyn faces an open revolt by parliamentary colleagues and UKIP leader Nigel Farage, one of the most effective Brexit campaigners, said he is resigning.

There has been a sharp drop in the pound and in British consumer confidence since the vote, while pro-EU Scotland is threatening to quit the United Kingdom.

"If things go well (at the time of the French elections), the FN will benefit from it. If it's trench warfare, if banks are moving their headquarters away from Britain, if the British economy has taken a hit, the FN argument will be caught out," Ifop pollsters' analyst Jerome Fourquet said.

The FN's Philippot says much of the talk about negative consequences of Brexit "is a refusal by the elite, especially in France, to accept reality."

But for Fourquet, "if the political situation in Britain unravels, if Scotland wants to leave ... the FN's opponents will be able to say: 'See, we've been telling you for years that the EU exit backed by Marine Le Pen, of which Brexit is a test case, is a failure."

JUMP OFF A MOVING TRAIN?

There is early evidence in some other European countries that the Brexit vote and the political uncertainty it triggered in Britain may be denting parties that want to leave the bloc.

Surveys conducted since the referendum have shown support for EU membership rising sharply in both Finland and Denmark.

"If the chaos we are witnessing in the UK at the moment makes others think twice about leaving, that is not a bad thing," an aide to German Chancellor Angela Merkel told Reuters.

It is unsure at this stage how clear the consequences of Brexit will be in 10 months' time, or whether the divorce talks will have started.

How Donald Trump's populist, anti-Washington message fares in U.S. election in November and whether the far-right wins in the October re-run of Austria's presidential election - which could itself be influenced by the Brexit vote - could also affect the FN's appeal.

Le Pen has said that, if elected, she would launch negotiations to leave the euro, restore borders, ensure the primacy of French law over EU law, and scrap EU checks on French public finances.

After six months, voters would decide in a referendum whether to stay in the bloc or leave.

Even within the FN, there has been criticism of this policy, which has put off the elderly - who tend to vote more than younger voters - for fear their pension could be affected.

However, opinion polls since the Brexit vote show a change among FN voters, with a huge majority now backing an EU exit. According to an OpinionWay survey on June 27, some 69 percent would vote for a "Frexit."

But those same polls also showed that only about one in three voters overall want a Frexit, making the FN's anti-EU stance an obstacle to voting for the otherwise increasingly popular party.

The head of the FN in Paris' Ile-de-France region, Wallerand de Saint Just, attributes this to a divide between richer and poorer voters.

"In the bourgeois neighborhoods, that's where it's a problem. They go crazy over these (EU) issues. That's what's stopping them from voting for us," Saint Just, who is also the FN's treasurer, told Reuters. "But in the working class areas they don't really care."

Analysts, who still see Le Pen losing the presidential election run-off, say it goes beyond this divide.

The French "are overall unhappy with how Europe works but many consider that once you are on a train, even if it's uncomfortable, it's dangerous to jump off a moving train," Fourquet said.

(Additional reporting by Noah Barkin in Berlin)