French leftist voters have reportedly engaged in a plot to derail far-right leader Marine Le Pen’s election bid by infiltrating the conservative primaries.

According to surveys, as many as 15 per cent of an electorate who brought socialist President François Hollande to power in 2012, will today sign a charter stating they share “Republican values of the Right and the Centre”, in an attempt to stop former president Nicolas Sarkozy from being nominated.

Many believe Mr Sarkozy could lose against Ms Le Pen in May’s presidential elections, and against the backdrop of the UK’s Brexit vote and Donald Trump’s US election win, some fear France could be next in line to confront the rise of global populism.

Left-voting business owner Violette Lacloche said she was not prepared to see that happen and would be voting for former prime minister Alain Juppé, who she believes would be a better contender against Ms Le Pen.

“In 2002, we left-wingers voted for Jacques Chirac to stop Jean-Marie Le Pen from becoming president,” Ms Lacloche told Politico.

“It’s the same thing this time around, just much sooner. We all know that the presidential election is being played out now.”

One 32-year-old Parisien, who wished only to be known as Amaury, said he would also be backing Mr Juppé.

“Polls are becoming less and less reliable and aren’t able to grasp people’s deepest convictions. I prefer to stay on the safe side and vote for Juppé,” he told Liberation.

Seven candidates are competing for position in Sunday’s primaries, and a second vote will be held next week to decide between the two frontrunners.

The three leading candidates are Mr Sarkozy and former prime ministers Francois Fillon and Mr Juppé.

Mr Sarkozy was said to be outraged by the leftist "coup", telling his supporters at a rally last week: "I will not let the Left steal this election from you!”

For many left-wing voters, Mr Trump’s shock election win was enough to motivate them to act early against the Front National.

“At one time, I was thinking voting for Juppé in the second round would be enough. But the election of Trump remotivated me. We need to protect our interests,” one voter told Liberation.

Nicolas Sarkozy, former French president and candidate for the French conservative presidential primary, votes in the first round of the French center-right presidential primary election in Paris, France, November 20, 2016 (REUTERS/Eric Feferberg/Pool)

However, some believe that even Mr Juppé, recognised as a moderate conservative, won’t be able to stop the “wave of populism”.

“The wave of populism could carry us into 2017. So can an old career politician like Juppé be the solution to this wave? Or will he be fated to be knocked out like Hillary Clinton, who became a figurehead for nothing other than the establishment?” Amaury said.

Many leftist voters who responded to a Politico survey admitted they would not want to be “outed” for voting in the conservative primaries, and many allegedly asked for anonymity.

In particular, prominent socialists and media personalities were said to be concerned about being branded "hypocrites" if they were caught entering a polling station.

However, left-wingers were not the only group rallying to hijack Sunday's Conservative vote.

Far-right supporters of Ms Le Pen’s party were also planning to turn out in high numbers, according to Politico.

Many believe Ms Le Pen could be edging ever closer to victory next spring, with French Prime Minister Manuel Valls warning of the dangers of electing a far-right president.

The far-right leader currently holds 29 per cent of the national vote when pitted against Les Républicains’ Nicolas Sarkozy, who is eight points behind, and holds a 15-point lead over the Left party’s Jean-Luc Mélenchon, in the latest poll released by Ipsos.