PARIS (Reuters) - Depending on who you ask, center-right presidential nominee Francois Fillon is either the perfect candidate to defeat the National Front, or the man whose economic radicalism will let France’s far right pose as protector of working class rights.

Francois Fillon, former French prime minister and member of Les Republicains political party, delivers his speech after partial results in the second round for the French center-right presidential primary election in Paris, France, November 27, 2016. REUTERS/Philippe Wojazer

The French presidential election, with a first round in April and a run-off in May, is on course to turn into another test of the rage of Western voters against traditional elites, after Britain’s shock vote to quit the EU and the U.S. election of Donald Trump as president.

Pollsters predict Fillon, a former prime minister who clinched the nomination of his Les Republicains party on Sunday, will face the far National Front’s Marine Le Pen in the run-off, casting him as the champion of the entire establishment against a surging far right that wants to follow Britain out of the EU.

But Fillon, a staunch Catholic conservative on social policy who models himself after Britain’s Margaret Thatcher on economic issues, is hardly typical of the French ruling elite, presenting unexpected challenges for Le Pen, but also opportunities.

On the one hand, Fillon won some of his best results in the primaries on Sunday in National Front (FN) strongholds. His social conservatism and tough stance on immigration steal some of the far right’s thunder. Le Pen’s personal approval ratings fell on the day.

On the other hand, Fillon’s hardline economic reform plan, which includes raising the retirement age, increasing the sales tax and lengthening working hours, could give Le Pen a chance to win over working class and even center-left voters with an appeal to economic principles seen as traditional in France.

Which of these two sides of Fillon’s platform will be more important to voters could decide whether France follows Britain and the United States in delivering an election surprise that overturns the established order.

The anti-migration, anti-Europe FN, which bills itself as the protector of the working classes, hit at both angles on Monday with the launch of its online campaign under the hashtag #TheTrueFillon.

“Francois Fillon in power would bring a terrible economic and social decline for families and for middle-class and working-class French,” Le Pen’s campaign director David Rachline said in a video sent to party supporters and posted on his Twitter feed. The online campaign targeted Fillon’s plans to shrink the public workforce, the sort of criticism that might normally come from the left.

But attacking simultaneously from the right, it questioned his credibility on immigration, calling him the “the establishment’s new star”.

Pollsters had expected the center-right would nominate a different former prime minister, the more traditional centrist Alain Juppe, setting up a conventional battle between the center and the far right.

The mild mannered Juppe might have had an easier time attracting center-left votes in a future run-off against Le Pen.

But Fillon’s late surge in the nomination contest saw him easily dispatch Juppe, creating a new dynamic.

The first survey published after the primaries, by Harris Interactive, sees Le Pen qualifying for the run-off and losing it to Fillon. But it showed her attracting just 24 percent of the votes in the first round, behind Fillon’s 26 percent, her lowest rating in months.

“Part of the FN electorate wants more protection from the state. But there is a part of the FN electorate that is very right wing, traditionalist, and Fillon can encroach on that electorate,” said Sylvain Crepon, a specialist on the FN at the French university of Tours.

“A GREAT CANDIDATE”?

Jerome Fourquet of Ifop pollsters said that while the FN had scored its strongest increase in regional elections last year amid the traditional Catholic electorate, surveys Ifop did on the first round of the primaries showed that those traditional Catholic voters who took part in the primaries massively backed Fillon.

The Les Republicains primaries were open to all voters. According to Fourquet, the small number of FN voters who took part backed Fillon ahead of Juppe or ex-president Nicolas Sarkozy, who was eliminated in a first round earlier this month.

In the Var area, a National Front stronghold where Le Pen’s campaign director Rachline is mayor, Fillon attracted 79.4 percent of the votes in the second round of the primaries, compared to 66.5 percent nationwide.

Opinion polls, which had failed to predict Fillon’s victory in the primaries until just days before the vote, are likely to evolve as the presidential campaign heats up and voters look in more detail at Fillon’s economic reform plans.

A survey by Odoxa showed that Fillon is doing well among voters with high-end jobs but struggling with working-class voters and public officials who are open to Le Pen, a weakness that could become a real issue for him during the campaign.

A majority of leftwing voters, wary of Fillon’s economic and social views, would not turn up to polling stations at all in the case of a Fillon-Le Pen second round, the poll said, a further difficulty for him.

“I voted for Fillon because he will never get leftwing voters on board,” 68-year old pensioner Denis Achard, an FN voter, said as he took part in the primaries on Sunday, tactically voting for the candidate he thought would be the easiest target for the FN.

Under the leadership of Marine Le Pen, who took over from her father Jean-Marie in 2011, the FN has switched from an economically liberal, pro-small business party to one that promises to lower the retirement age and guarantee France’s generous welfare safety net.

Fillon’s victory in the primaries risks exacerbating the tensions between that line, backed by Le Pen and her deputy Florian Philippot, and a pro-business, anti-big state line spearheaded by Le Pen’s niece Marion Marechal-Le Pen.

While Philippot told Reuters Fillon is a “great candidate” for the FN because of his economic plans, Marechal-Le Pen raised the possibility of him being a tougher candidate to beat.

“We should have been alerted by the signals he sent to the Catholics and the non-mainstream right,” French media quoted her as saying.