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 €82,000 between them as assistants when he was a senator.