Former French prime minister Francois Fillon will win the conservative nomination for next year's presidential election by a wide margin, an Ifop-Fiducial poll forecast ahead of a run-off vote on Sunday.

Fillon, a 62-year-old social conservative with economically liberal ideas who admires late British prime minister Margaret Thatcher, unexpectedly topped the first round of the primaries last Sunday.

He would win the second round with 65 percent of votes versus 35 percent for Alain Juppe, another ex-prime minister who had for months been ahead in the opinion polls, the Ifop-Fiducial survey showed.

Considering the divisions of the Left and deep unpopularity of Socialist President Francois Hollande, the winner of the run-off has a strong chance of being elected president in May.

Anyone can take part in the primaries, whether they are members of the Les Republicains conservative party or not.

The poll showed Fillon, whose pro-Russian stance is raising eyebrows in Berlin, is set to get over three-quarters of the votes of those who cast a ballot last Sunday for ex-president Nicolas Sarkozy, who failed to qualify for the run-off.

Some 75 percent of sympathizers of Les Republicains will vote for Fillon, and 84 percent of those sympathizers of the far-right National Front party who intend to take part in the vote will also back Fillon, the poll showed.

Juppe is set to get 83 percent of the votes of left-wing voters and 66 percent of votes of centrist party sympathizers, the poll said.

Some 6,901 people were interviewed on Nov. 21-23 for the iTELE, Paris Match and Sud Radio poll. The results only take into account the 619 people surveyed who said they were certain to vote this Sunday.

Another survey by Elabe pollsters showed that while conservative and center-right voters overwhelmingly liked Fillon's policies better than Juppe's, the latter is more popular among the French overall, in a sign that Fillon could struggle more than his rival in a presidential election run-off.

Polls have for months predicted that National Front party leader Marine Le Pen would fare well in the first round of the presidential election on April 23 and qualify for the second round.

There have been no polls this month on the May 7 run-off but previous polls forecast that Le Pen would lose it to a mainstream, conservative candidate.

After Fillon's unexpected win and the surprise victories of President-elect Donald Trump in the United States and Britain's vote to leave the European Union, voters and commentators are increasingly skeptical about opinion poll predictions.