Emmanuel Macron's position as favourite in France's presidential election was boosted on Thursday by an opinion poll which showed him beating far-right leader Marine Le Pen in both the first and final rounds of the two-stage contest.

The Harris Interactive poll showed Macron winning the first round with 26 per cent of votes, with Le Pen taking second place on 25 per cent, sending the two to a May 7 run-off where he would trounce her with a score of 65 per cent.

It was the second poll in the space of a week that put the 39-year-old ahead of Le Pen in the opening round, a signal that the centrist former economy minister may be consolidating his position 45 days from leg-one of the contest.

The race remains difficult to call, however, after a string of surprises, including Socialist incumbent Francois Hollande's decision not to seek a second-term, and shock wins in primaries for contenders the pollsters had ruled out.

Additionally, financial scandals have engulfed Le Pen and conservative Francois Fillon, who after his surprise victory in the primary of The Republicans party as recently as January the clear poll favourite to become president.

In the latest poll, Fillon, who is struggling to relaunch a campaign derailed by a judicial investigation into allegations he lavishly paid his wife for minimal work as an assistant, comes third in the first round on 20 per cent.

That would eliminate the erstwhile frontrunner. Were he to catch up in the weeks ahead and secure a place in the run-off versus Le Pen, the 63-year-old former prime minister would also beat her with a score of 59 percent.

Le Pen slippage

In both second-round scenarios, the margin by which Le Pen loses is wider than in some recent polls.

Le Pen's campaign head, David Rachline, dismissed Thursday's poll news, saying in reference to round one: “The reality right now is that Marine (Le Pen) is in front in almost all polls.”

While Le Pen's score was unchanged from the last time the Harris poll was conducted two weeks ago, Macron's surged six percentage points. In that period he unveiled his campaign manifesto and veteran centrist Francois Bayrou gave him his support.

The latest Harris survey, conducted on March 6-8 with a sample of 4,932 voters, also showed that while Macron voters were still the most undecided among those backing leading candidates, the proportion who were sure they would vote for him had risen by 10 percentage points to 59 per cent.

The publication on Thursday coincided with the release of a research note from Credit Suisse bank that said the risk of a win for Le Pen, who wants to restore the French franc currency, was exaggerated.

Credit Suisse equity strategists raised their recommendation on investment in French equities - in technical jargon to “small overweight” from a lesser “benchmark", partly on a belief that Le Pen would lose.

“We think the risk of a Le Pen victory is overestimated," they wrote. “The 30 per cent chance priced in betting markets is too high in our view,” they added.

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