On a busy shopping street in the Paris constituency of the scandal-hit French presidential candidate François Fillon, the word corruption was creeping into the smalltalk.

“All French politicians are corrupt,” said a 52-year-old pharmacist, sighing. “Some scandals come to light, others stay hidden, but 100% of politicians are up to no good – everywhere, not only in France.”

Corruption allegations and investigations are plaguing the French presidential election: police raids have dominated headlines, distracting from policy debate and exacerbating a sense of disillusionment with the political class.

First Fillon, who had campaigned as a sleaze-free “Mr Clean”, was alleged to have paid his wife, Penelope, who is British, at least €680,000 of taxpayers’ money for a suspected fake parliamentary assistant job spanning 15 years. Then financial prosecutors extended their investigation into allegations that he also gave his children highly paid fake jobs from state funds. On Friday night, an investigating magistrate was appointed to head a full judicial inquiry.

Next, the far-right Front National’s Marine Le Pen – who polls say will certainly make it to the final round in May – was hit by new moves in a French investigation into whether her party misused more than €300,000 in European public funds to illegally pay her French party workers from the European parliament kitty.

On Friday Le Pen refused to attend a summons for police questioning in the case until after the presidential vote and the parliamentary elections that follow in June. Her party headquarters were raided this week by police. Two close staff – her bodyguard and personal assistant – were questioned by investigators.

The impact of these scandals on the electorate has so far been very different: where Fillon has been wounded, Le Pen is unshaken.

Both have denied all allegations against them. They have also adopted a “victimisation” defence – previously used by Nicolas Sarkozy when he was faced with several campaign-funding investigations. They say they are the target of underhand plots by their political opponents.

Fillon has seen his poll ratings dip, his image badly hurt, public appearances heckled and morale drop among his party grassroots on the campaign trail – even though he has vowed to soldier on whether or not he is charged.

Le Pen meanwhile continues to have a strong lead in the first-round vote, ahead of the independent centrist Emmanuel Macron with Fillon behind, although polls show her losing the second round. Her supporters – who polls show are more resolved and committed than any other voters – have rallied behind her.

Who is Emmanuel Macron? The 39-year-old was raised in Picardy, studied philosophy and was briefly a rising star in the the civil service before joining Rothschild as an investment banker. He served François Hollande first as senior adviser then as economy minister, before resigning and launching his campaign. Macron defines himself as an energetic outsider, 'of the left' and progressive on social issues, but economically liberal and pro-business. His youthful movement En Marche! (Let’s Go!) draws thousands to its rallies. Opponents say his crusade to reinvent the political system is presumptuous and have criticised his deliberately flexible approach to policy. Read our profile

The FN has faced three legal issues in the last year: allegations of misuse of European parliament funds; an investigation into alleged fraudulent campaign financing in France by overcharging candidates for election material; and an investigation into whether Le Pen and her father, Jean-Marie, underestimated the value of their personal property in their declaration of interests as MEPs.

The FN leader denies all the allegations. She is described as the “Teflon candidate” – the accusations slide off her without denting her vote.

“The reactions of French voters in this campaign are unpredictable, and maybe things will evolve, but for the moment, Le Pen is totally untouched by this,” said Jean Garrigues, political historian and author of Elysée Circus, a book about presidential campaigns.

“There are several reasons Le Pen is untouched,” said Garrigues. “First, the nature of the allegations: the European parliament case is about party funding, not the personal enrichment of Le Pen herself. That is an important distinction.

“Second, among Front National voters, there is a very strong reflex of self-defence and victimisation – a firm idea that there is a plot by the politicians in power and the system against them. And also, there is a certain indulgence towards Le Pen – her supporters feel they need her to stand up to the system.”

Thousands protested in Paris and cities across France last weekend, with banners reading “Jail the corrupt” and “Down with the privileged”, and there is a newfound soul-searching and anger in France about corruption among the political class.

What might be accepted 10 years ago is no longer accepted today, because the country is in economic and social crisis Jean Garrigues

For decades, France was seen as a nation where corruption allegations did nothing to stop a high-flying political career. The clearest example was Jacques Chirac who rose to serve two terms as president before finally in 2011 receiving a two-year suspended prison sentence for embezzling public funds to illegally finance his rightwing party.

At the local and parliament level, there was a habit of re-electing politicians despite ongoing corruption investigations – described by the former Green presidential candidate and one-time anti-corruption magistrate Eva Joly as a dangerous culture of “the lawmaker as law-breaker”.

During François Hollande’s presidency a massive political corruption scandal was seen as the final straw, and new investigative powers and checks and balances were ushered in. Jérôme Cahuzac, the minister who led Hollande’s drive for a more honest tax system, was sentenced to three years in prison for tax fraud and secretly stashing his wealth in tax havens around the world.

Garrigues said that while there was once a “tradition of cynicism and resignation” among French people towards corruption in politics, there was now a much higher demand for ethics. “What might be accepted 10 years ago is no longer accepted today, because the country is in economic and social crisis, and there is a crisis of confidence in politicians.”

The 2017 presidential election result is unpredictable: about half of voters are still undecided. Fillon hopes his image of soldiering on against plotters will rally enough of his core supporters on the right, but this is uncertain. Polls show Le Pen’s voters are the least likely to waver. Macron, recently joined by veteran centrist François Bayrou, is expected to put forward measures to clean up French politics.

In Fillon’s constituency, Annick, 77, a retired shopworker, said her Catholic family was disappointed in Fillon after placing so much hope in him as “a decent man” – but she would still vote for him, because she “can’t see any other option for sorting out France’s economic problems”.

Her real fear, Annick said, was that “the person who will benefit from all of this is Marine Le Pen”.