French rightwing candidate was favourite to win but latest poll shows him being eliminated in first round as backlash grows

François Fillon is battling to save his rightwing bid for the French presidency as party colleagues increased pressure on him to stand aside after fresh allegations he paid his family large amounts of taxpayers’ money.

Fillon was considered a favourite to win the two-round presidential election in April and May. But for the first time since allegations broke last week that he had paid his wife for an allegedly fake job as a parliamentary assistant, a poll showed him sinking and being eliminated in the first round, lagging behind the far-right Marine Le Pen and overtaken by the centrist, maverick independent Emmanuel Macron.

MPs in Fillon’s party, Les Républicains, began to question whether he was becoming an electoral liability, after having built his campaign on a carefully crafted image as a sleaze-free honourable country gentleman who wanted to slash public spending and cut public jobs.

One poll showed 76% of French voters were not convinced by his response to the scandal.

Fillon has denied the allegations and insists he will not pull out of the presidential race unless he is charged with an offence. He is alleged by the investigative paper Le Canard Enchaîné to have paid his British wife Penelope about €830,000 (£700,000) as a parliamentary assistant for more than a decade – a higher amount than previously thought.

It is legal for French MPs to hire family members, as long as the person is genuinely employed. But French prosecutors have launched a preliminary investigation into the possible “misuse of public funds” to determine whether or not Penelope Fillon had in fact done any work for her husband.

The Canard Enchaîné also revealed on Wednesday that Fillon had paid his two children €84,000 between them as assistants when he was a senator.

Fillon urged MPs at a closed meeting on Wednesday to stick by him at least for another two weeks as the investigation continued. He vowed he would remain as candidate and fight “to the end”.

But he continued to argue he was the victim of a plot, accusing the current Socialist government of staging an “institutional coup d’état” against him.

An aide to the Socialist president François Hollande dismissed the allegation, saying: “The only power is that of the justice system.”

Officially, Les Républicains party is not yet looking for a possible replacement if Fillon is forced to drop out, but the nervousness behind the scenes was palpable.

MPs are worried voters in their constituencies will turn away from the party not just in the presidential race but in the crucial parliamentary election that follows in June.

The electorate has little patience for a political class it instinctively distrusts and many are wary of what they sees as undue perks and privileges available to politicians.

Georges Fenech, Les Républicains MP for the Rhône, told France Info radio that Fillon’s nomination as the presidential candidate was “null and void” in the light of these unforeseen circumstances. He said Fillon’s situation was “no longer tenable”.

Facebook Twitter Pinterest An issue of Le Canard Enchaîné is displayed among other newspapers in a kiosk in Paris. Photograph: Yoan Valat/EPA

He said it was question of “ethics and morals”. The party could not just sit there, “like the orchestra on the Titanic as it sinks”.

Another MP, Bruno Le Maire, who had also run in the primary race to choose a candidate, admitted that the amount of money in question in the scandal “shocked a lot of French people”.

It remains uncertain how the party could go about finding another candidate if the situation arises. Fillon won the primary race outright against Alain Juppé, knocking out the former president Nicolas Sarkozy in the first round. There is no time for another primary race.

Juppé said last week he wouldn’t be a standby candidate, but that could change. New faces have been mooted by French media, including former minister, François Baroin; the head of the northern Hauts-de-France region, Xavier Bertrand; or the head of the Ile-de-France region around Paris, Valérie Pécresse.

Fillon is under pressure over various separate issues as well as inconsistencies in his public declarations. The Canard Enchaîné reported on Wednesday that he had paid his wife for more years than he said last week in a TV interview.

He also said on TV that as a senator he paid two of his children to assist him because they were lawyers. However it has emerged they were students and not qualified at the time. The newsweekly L’Obs on Wednesday headlined an article: “François Fillon: Super-Liar”.

Prosecutors are also investigating a second job in which the Canard Enchaîné claimed Penelope Fillon was paid large sums between 2012 and 2013 by a literary review owned by a billionaire businessman friend of Fillon, but where she was alleged to have only written two book reviews.

Fillon denied any wrongdoing and insisted her consultancy job was real.

The investigative website Mediapart and the newspaper Journal du Dimanche have also claimed that Fillon pocketed €25,000 in funds earmarked for senate assistants between 2005 and 2007. Fillon’s allies dismissed the claims.

Meanwhile, there is renewed public interest in a consulting firm Fillon set up in 2012 at the end of his five-year term as prime minister. The Canard Enchaîné reported that the consultancy had paid Fillon an after-tax salary of €757,000 since 2012. Opponents are demanding he reveal the source of the money.